Liquid crystal display and method of manufacturing the same

ABSTRACT

A liquid crystal display including two substrates, gate bus lines, liquid crystal molecules, and a polymer that determines directions in which the liquid crystal molecules tilt. A plurality of divisional areas are arranged on one of the substrates. The pixels are aligned in a column between drain bus lines. A pixel electrode is formed at each of the divisional areas. A first thin film transistor drives a first divisional area, and a second thin film transistor drives a second divisional area of the same column. The first and second thin film transistors are electrically connected to the same gate bus line. Either the pixel electrodes formed at each of the divisional areas are electrically insulated from each other, or they are connected to each other through a high resistance. A first threshold voltage within the first divisional area is different from a second threshold voltage of the second divisional area.

This is a divisional of application Ser. No. 12/827,030, filed Jun. 30,2010, which is a divisional of application Ser. No. 11/299,799, filedDec. 12, 2005, which is a divisional of application Ser. No. 10/796,783,filed Mar. 9, 2004, now U.S. Pat. No. 7,262,824, which issued on Aug.28, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display used as adisplay section of an electronic apparatus and a method of manufacturingthe same, and more particularly to an MVA type liquid crystal displayhaving high viewing angle characteristics and a method of manufacturingthe same.

2. Description of the Related Art

Recently, liquid crystal displays are widely used in variousapplications taking advantage of their features such as low profiles andlight weights, low-voltage drivability and low power consumption.Further, some liquid crystal displays are available with displaycharacteristics comparable to those of CRTs and are therefore being putin use as monitors and television receivers for which CRTs have beendominantly used.

Among liquid crystal displays that are currently in practical use, MVA(Multi-domain Vertical Alignment) displays are one of types whichexhibit high display characteristics comparable to those of CRTs. In anMVA type liquid crystal display (hereinafter referred to as “MVA-LCD”),liquid crystal molecules are aligned substantially perpendicularly to asubstrate surface when no voltage is applied. When a voltage is applied,the liquid crystal molecules are aligned in a predetermined directionthat is regulated by alignment regulating structures formed on asubstrate surface. Alignment regulating structures include protrusions,recesses, and blanks (slits) in an electrode.

FIG. 37 shows a configuration of three pixels of a common MVA-LCD. Asshown in FIG. 37, linear protrusions 1102 and 1104 in a zigzagconfiguration constituted by dielectric bodies are formed on a pair ofsubstrates provided opposite to each other, respectively. The linearprotrusions 1102 formed on one of the substrates and the linearprotrusions 1104 formed on the other substrate are disposed alternately.Thus, liquid crystal molecules are tilted in a different direction ineach of regions A, B, C and D. Liquid crystal molecules in one pixel aretilted in four directions in the regions A, B, C and D, respectively,each of the directions being at a differential angle of about 90°. Thus,four domains of alignment are obtained.

-   Patent Document 1: JP-A-2000-356773-   Patent Document 2: JP-A-2002-357830-   Patent Document 3: Japanese Patent No. 2947350-   Patent Document 4: JP-A-H11-242225

FIG. 38A is a graph showing transmittance-voltage characteristics (T-Vcharacteristics) of the MVA-LCD shown in FIG. 37. The abscissa axisrepresents voltages (V) applied to the liquid crystal, and the ordinateaxis represents transmittances (%) of light. The line X1 in the graphindicates T-V characteristics in a direction perpendicular to thedisplay screen (hereinafter referred to as “square direction”), and theline X2 indicates T-V characteristics in an upward direction at a polarangle of 60° to the display screen (hereinafter referred to as “obliquedirection”). A polar angle is an angle to a line perpendicular to thedisplay screen. The display mode of the MVA-LCD is the normally blackmode in which a voltage (absolute value) applied to the liquid crystalis decreased to display black and increased to display white. As shownin FIG. 38A, when voltages (in the range from about 2.2 to 2.9 V) in theneighborhood of a region where a threshold voltage is exceeded areapplied, transmittances in the oblique direction are higher than thosein the square direction.

FIG. 38B is an enlarged view of the neighborhood of the thresholdvoltage in the graph shown in FIG. 38A. As shown in FIG. 38B, forexample, when a voltage (about 2.3 V) which provides a transmittance of0.2% in the square direction is applied, transmittance in the obliquedirection increases to about 2.5% as indicated by the arrow in thefigure. In particular, when a voltage slightly in the excess of thethreshold voltage is applied, since the value of the resultanttransmittance itself is small, transmittance in the oblique directionincreases significantly relative to transmittance in the squaredirection. This results in a problem in that an image displayed inhalftones appears whitish in the oblique direction because ofdegradation of gradation/viewing angle characteristics. It is desired tomitigate this phenomenon because it can reduce display quality of anMVA-LCD.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a liquid crystal displaywhich can achieve high viewing angle characteristics and a method ofmanufacturing the same.

The above object is achieved by a liquid crystal display characterizedin that it has a pair of substrates provided opposite to each other, aliquid crystal sealed between the pair of substrates, alignmentregulating structures formed on at least either of the pair ofsubstrates for regulating the alignment of the liquid crystal, and aplurality of pixel regions having both of a first area in which thealignment regulating structures are disposed at first intervals andwhich has a first threshold voltage for driving of the liquid crystaland a second area in which the alignment regulating structures aredisposed at second intervals smaller than the first intervals and whichhas a second threshold voltage lower than the first threshold voltage.

As described above, the invention makes it possible to provide a liquidcrystal display which can achieve high viewing angle characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are graphs showing T-V characteristics of a liquidcrystal display in a first mode for carrying out the invention;

FIG. 2 shows a schematic configuration of the liquid crystal display inthe first mode for carrying out the invention;

FIG. 3 is a sectional view showing a configuration of an MVA-LCD;

FIG. 4 is a graph showing T-V characteristics of the MVA-LCD;

FIGS. 5A to 5F show examples of patterns in which alignment regulatingstructures are disposed;

FIG. 6 is a sectional view showing disposition of protrusions in apixel;

FIG. 7 shows disposition of protrusions in a pixel as viewed in adirection perpendicular to substrate surfaces;

FIG. 8 is a graph showing a comparison between T-V characteristicsachieved with the configuration shown in FIG. 6 and T-V characteristicsachieved with the configuration shown in FIG. 7;

FIG. 9 shows a configuration of a liquid crystal display according toEmbodiment 1-1 in the first mode for carrying out the invention;

FIG. 10 shows a configuration of a liquid crystal display according toEmbodiment 1-2 in the first mode for carrying out the invention;

FIG. 11 shows a configuration of a liquid crystal display according toEmbodiment 1-3 in the first mode for carrying out the invention;

FIG. 12 is a sectional view showing a configuration of a liquid crystaldisplay in a second mode for carrying out the invention;

FIG. 13 is a graph showing T-V characteristics of the liquid crystaldisplay in the second mode for carrying out the invention;

FIG. 14 is a sectional view showing another configuration of a liquidcrystal display in the second mode for carrying out the invention;

FIGS. 15A to 15F are sectional views taken in processes showing a methodof manufacturing a liquid crystal display according to the related art;

FIGS. 16A to 16C are sectional views taken in processes showing a methodof manufacturing a liquid crystal display in the second mode forcarrying out the invention;

FIGS. 17A to 17C are sectional views showing the flow of the formationof alignment controlling layers;

FIGS. 18A and 18B are sectional views showing a method of formingalignment controlling layers having different anchoring energies in onepixel;

FIG. 19 is a sectional view showing another example of a method offorming alignment controlling layers having different anchoring energiesin one pixel;

FIG. 20 is a sectional view showing still another example of a method offorming alignment controlling layers having different anchoring energiesin one pixel;

FIG. 21 is a graph showing dependence of a T-V curve on the dose ofirradiation with light;

FIG. 22 is a graph showing dependence of T-V characteristics on the doseof irradiation with light in a case wherein an optical initiator isused;

FIG. 23 is a sectional view showing a configuration of a liquid crystaldisplay fabricated according to a method of manufacturing a liquidcrystal display in the second mode for carrying out the invention;

FIG. 24 is a sectional view showing a configuration of a liquid crystaldisplay fabricated according to the method of manufacturing a liquidcrystal display in the second mode for carrying out the invention;

FIG. 25 is a sectional view showing a configuration of a liquid crystaldisplay fabricated according to the method of manufacturing a liquidcrystal display in the second mode for carrying out the invention;

FIG. 26 is a sectional view showing a configuration of a liquid crystaldisplay fabricated according to the method of manufacturing a liquidcrystal display in the second mode for carrying out the invention;

FIG. 27 is a graph showing T-V characteristics in an area havingalignment controlling layers and showing T-V characteristics in an areahaving vertical alignment films formed therein;

FIG. 28 shows a schematic sectional configuration of an MVA-LCD;

FIG. 29 shows a schematic sectional configuration of an IPS mode liquidcrystal display;

FIG. 30 is a sectional view of a region substantially equivalent to onepixel showing a configuration of a liquid crystal display in a thirdmode for carrying our the invention.

FIG. 31 is a sectional view of a region substantially equivalent to onepixel showing a pre-tilt angle of liquid crystal molecules of the liquidcrystal display in the third mode for carrying out the invention;

FIG. 32 is a graph showing T-V characteristics of the liquid crystaldisplay in the third mode for carrying out the invention;

FIG. 33 is a sectional view of a region substantially equivalent to onepixel showing a configuration of a liquid crystal display according toEmbodiment 3-1 in the third mode for carrying out the invention;

FIG. 34 is a graph showing how a voltage applied to a liquid crystal ofEmbodiment 3-1 in the third mode for carrying out the invention changeswith time;

FIG. 35 shows a sectional configuration of a liquid crystal displaywhich has areas with a different initial pre-tilt angle in some partsthereof;

FIG. 36 shows a sectional configuration of a liquid crystal displayhaving slits formed therein;

FIG. 37 shows a configuration of a liquid crystal display according tothe related art;

FIGS. 38A and 38B are graphs showing T-V characteristics of the liquidcrystal display according to the related art;

FIG. 39 schematically shows a configuration of a liquid crystal displaywhich constitutes a base of a fourth mode for carrying out theinvention;

FIG. 40 is a sectional view showing a configuration of a liquid crystaldisplay panel which constitutes a base of the fourth mode for carryingout the invention;

FIG. 41 shows an equivalent circuit of one pixel of a liquid crystaldisplay in the fourth mode for carrying out the invention;

FIG. 42 shows a configuration of a liquid crystal display according toEmbodiment 4-1 in the fourth mode for carrying out the invention;

FIG. 43 shows an equivalent circuit of one pixel of the liquid crystaldisplay according to Embodiment 4-1 in the fourth mode for carrying outthe invention;

FIG. 44 shows a modification of the configuration of the liquid crystaldisplay of Embodiment 4-1 in the fourth mode for carrying out theinvention;

FIG. 45 shows another modification of the configuration of the liquidcrystal display of Embodiment 4-1 in the fourth mode for carrying outthe invention;

FIG. 46 shows still another modification of the configuration of theliquid crystal display of Embodiment 4-1 in the fourth mode for carryingout the invention;

FIG. 47 shows an equivalent circuit of one pixel of a liquid crystaldisplay according to Embodiment 4-2 in the fourth mode for carrying outthe invention;

FIG. 48 shows an equivalent circuit of one pixel of a liquid crystaldisplay according to Embodiment 4-3 in the fourth mode for carrying outthe invention;

FIG. 49 shows an equivalent circuit of one pixel of a liquid crystaldisplay according to Embodiment 4-4 in the fourth mode for carrying outthe invention;

FIG. 50 shows a configuration of a liquid crystal display fabricatedusing a method of manufacturing a liquid crystal display according toEmbodiment 5-1 in a fifth mode for carrying out the invention;

FIG. 51 is a sectional view showing a schematic configuration of theliquid crystal display taken along the line A-A in FIG. 50;

FIGS. 52A to 52D are sectional views showing the method of manufacturingthe liquid crystal display according to Embodiment 5-1 in the fifth modefor carrying out the invention;

FIGS. 53A to 53D are sectional views showing a method of manufacturing aliquid crystal display according to Embodiment 5-2 in the fifth mode forcarrying out the invention;

FIGS. 54A to 54D are sectional views showing a method of manufacturing aliquid crystal display according to Embodiment 5-3 in the fifth mode forcarrying out the invention;

FIGS. 55A to 55D are sectional views showing a method of manufacturing aliquid crystal display according to Embodiment 5-4 in the fifth mode forcarrying out the invention;

FIG. 56 shows a sectional shape of a liquid crystal display;

FIG. 57 shows an example of an electrode pattern of an MVA type liquidcrystal display according to the related art;

FIGS. 58A and 58B illustrate alignment control exercised by structuresof an MVA type liquid crystal display;

FIG. 59 shows another example of structures (electrode slits);

FIG. 60 shows a difference in applied voltage/transmittance (T-V)characteristics of an MVA type liquid crystal display according to therelated art depending on the viewing angle;

FIG. 61 illustrates the principle of an HT method for improving viewingangle characteristics by providing parts having different thresholdvoltages in one pixel;

FIGS. 62A and 62B illustrate a definition of the disposing density ofstructures (protrusions);

FIG. 63 shows a difference in T-V characteristics attributable tointervals between protrusions in a configuration in which theprotrusions are disposed on both substrates;

FIG. 64 shows changes in a threshold voltage attributable to intervalsbetween protrusions;

FIGS. 65A and 65B illustrate different aligning operations that dependon intervals between protrusions;

FIG. 66 shows a difference in T-V characteristics attributable tointervals between protrusions in a configuration in which theprotrusions are disposed on one substrate;

FIGS. 67A to 67C illustrate behaviors of liquid crystal molecules in anarea in which an interval between protrusions is small;

FIGS. 68A to 68C show examples of disposition of protrusions accordingto Embodiment 6-1 in a sixth mode for carrying out the invention;

FIGS. 69A and 69B show configurations and patterns of the protrusions ofEmbodiment 6-1 in the sixth mode for carrying out the invention;

FIG. 70 shows T-V characteristics of Embodiment 6-1 in the sixth modefor carrying out the invention;

FIG. 71 shows configurations and patterns of protrusions according toEmbodiment 6-2 in the sixth mode for carrying out the invention;

FIG. 72 shows configurations and patterns of other structures accordingto Embodiment 6-2 in the sixth mode for carrying out the invention; and

FIG. 73 shows another example of structures (recesses).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Mode forCarrying Out the Invention

A liquid crystal display in a first mode for carrying out the inventionwill be described with reference to FIGS. 1A to 10. First, a techniquewhich constitutes the basis of the present mode for carrying out theinvention will be described. One method for solving the problem that adisplayed image appears whitish in an oblique direction is a techniquein which both of areas having different threshold voltages are providedin one pixel. For example, an area having a threshold voltage (about 2.2V) as shown in FIGS. 38A and 38B and an area having a threshold voltagelower than the same are both provided in one pixel. FIG. 1A is a graphshowing T-V characteristics of an MVA-LCD utilizing the above-describedtechnique. FIG. 1B is an enlarged view of the neighborhood of athreshold voltage in the graph shown in FIG. 1A. The abscissa axisrepresents voltages (V) applied to the liquid crystal, and the ordinateaxis represents light transmittances (%). The line A1 in the graphindicates T-V characteristics in a square direction and, the line A2indicates T-V characteristics in an oblique direction.

As shown in FIGS. 1A and 1B, when a voltage that provides atransmittance of 0.2% in the square direction is applied, thetransmittance in the oblique direction increases to about 0.7% asindicated by the arrow in FIG. 1B. The transmittance in the obliquedirection can be suppressed to one-thirds or less of that of the MVA LCDaccording to the related art shown in FIGS. 38A and 38B, which is asignificant improvement in display quality. This technique makes itpossible to suppress the increase in transmittance in the obliquedirection relative to transmittance in the square direction, therebyimproving display quality significantly. The provision of an area havinga low threshold voltage in addition to an area having a normal thresholdvoltage is advantages also in suppressing any increase in a drivingvoltage of a liquid crystal.

The liquid crystal display in the present mode for carrying out theinvention will now be described. FIG. 2 shows a schematic configurationof the liquid crystal display in the present mode for carrying out theinvention. As shown in FIG. 2, the liquid crystal display has gate buslines and data bus lines formed such that they intersect each other withan insulation film interposed between them and a TFT substrate 2 havinga TFT and a pixel electrode formed at each pixel. The liquid crystaldisplay also has an opposite substrate 4 having a common electrodeformed thereon and a liquid crystal (not shown) sealed between thesubstrates 2 and 4.

A gate bus line driving circuit 80 loaded with a driver IC for drivingthe plurality of gate bus lines and a data bus line driving circuit 82loaded with a driver IC for driving the plurality of data bus lines areprovided on the TFT substrate 2. The driving circuits 80 and 82 outputscan signals and data signals to predetermined gate bus lines and databus lines based on predetermined signals output by a control circuit 84.A polarizer 86 is provided on a surface of the TFT substrate 2 oppositeto the surface where the elements are formed, and a backlight unit 88 isattached to a surface of the polarizer 86 opposite to the TFT substrate2. A polarizer 87 in a crossed Nicols relationship with the polarizer 86is attached to a surface of the opposite substrate 4 opposite to thesurface on which the common electrode is formed.

In order to decrease a threshold voltage of the MVA-LCD, it is effectiveto make intervals between alignment regulating structures smaller. FIG.3 shows a schematic sectional configuration of the MVA-LCD. As shown inFIG. 3, the TFT substrate 2 has a pixel electrode 16 formed at eachpixel region on a glass substrate 10. A plurality of linear protrusions44 which are alignment regulating structures for regulating thealignment of the liquid crystal are formed in parallel with each otheron the pixel electrode 16. On the contrary, the opposite substrate 4 hasa common electrode 42 which is formed substantially on an entire surfaceof a glass substrate 11. A plurality of linear protrusions 45 are formedin parallel with each other on the common electrode 42. The protrusions44 and 45 are alternately arranged when viewed in a directionperpendicular to the surfaces of the substrates. In a common MVA-LCD,the width of the protrusions 44 and 45 is, for example, 10 μm, andintervals a between edges of the protrusions 44 and respective edges ofthe protrusions 45 are, for example, 25 μm.

FIG. 4 is a graph showing T-V characteristics of the MVA LCD. The lineB1 in the graph indicates T-V characteristics achieved when theintervals a between the protrusions 44 and 45 are 25 μm, and the line B2indicates T-V characteristics achieved when the intervals a are 7.5 μm.As shown in FIG. 4, whereas the threshold voltage is about 2.1 V whenthe intervals a are 25 μm, the threshold voltage is about 1.7 V when theintervals a are 7.5 μm. Thus, the threshold voltage can be lower, thesmaller the intervals a between the protrusions 44 and 45. That is, bothof areas having different threshold voltages can be provided in onepixel by forming areas having different intervals a in the single pixel.

When a threshold voltage difference between the areas having differentthreshold voltages is 0.3 V or more, the effect of the invention ofimproving viewing angle characteristics can be achieved. Preferably, asignificant effect is achieved at a threshold voltage difference of 0.5V or more, and a very significant improvement is achieved at adifference of 0.7 V or more.

FIGS. 5A to 5F show examples of patterns of disposition of alignmentregulating structures in the area in which the intervals a are small andin which the threshold voltage is low. In the example shown in FIG. 5A,grid-like protrusions 44 are formed on the TFT substrate 2, andgrid-like protrusions 45 are formed on the opposite substrate 4 with anoffset from the protrusions 44 by half a pitch.

In the example shown in FIG. 5B, a point-like protrusion 44 is formed onthe TFT substrate 2. Grid-like protrusions 45 are formed on the oppositesubstrate 4. The point-like protrusion 44 is disposed substantially inthe middle of a gap between the grid-like protrusions 45.

In the example shown in FIG. 5C, a point-like electrode blank (slit) 46is formed on the TFT substrate 2 instead of the protrusion 44 shown inFIG. 5B.

In the example shown in FIG. 5D, grid-like slits 46 are formed on theTFT substrate 2. A point-like protrusion 45 is formed on the oppositesubstrate 4. The point like protrusion 45 is disposed substantially inthe middle of a gap between the grid-like slits 46 (that is, a regionwhere an electrode is formed).

In the example shown in FIG. 5E, the opposite substrate 4 is formed withgrid-like protrusions 45 and a point-like protrusion 45′ disposedsubstantially in the middle of a gap between the protrusions 45. Aframe-like protrusion 44 is formed between the protrusions 45 and 45′ onthe TFT substrate 2.

In the example shown in FIG. 5F, frame-like slits 46 are formed on theTFT substrate 2 instead of the protrusion 44 shown in FIG. 5E.

In the configurations shown in FIGS. 5A to 5F, liquid crystal molecules8 are radially tilted in four directions each of which is at adifferential angle of about 90°. The intervals a of alignment regulatingstructures are desirably 15 μm or less in an area having small intervalsa and a low threshold voltage in a pixel region. Intervals a of 15 μm orless result in a significant effect of improving viewing anglecharacteristics because they provide a significant effect of decreasingthe threshold voltage of the liquid crystal. The invention is notlimited to those patterns of disposition of alignment regulatingstructures.

FIG. 6 is a sectional view showing disposition of protrusions in apixel. As shown in FIG. 6, linear protrusions 44 and 45 formed inparallel with each other are disposed at intervals of 25 μm.

FIG. 7 shows disposition of protrusions formed in a pattern differentfrom that of the protrusions shown in FIG. 6, the disposition beingshown in a direction perpendicular to substrate surfaces. As shown inFIG. 7, grid-like protrusions 45 having a width 5 μm and a substantiallysquare protrusion 45′ having a width of 8 μm are formed on the oppositesubstrate 4. A frame-like protrusion 44 having a width of 5 μm is formedon the TFT substrate 2. The intervals between the protrusions 44 and 45′and the intervals between the protrusions 44 and 45 are both 6 μm andare smaller than the intervals of 25 μm between the protrusions 44 and45 shown in FIG. 6.

FIG. 8 is a graph showing a comparison between T-V characteristicsachieved with the configuration shown in FIG. 6 and T-V characteristicsachieved with the configuration shown in FIG. 7. The line C1 in thegraph indicates the T-V characteristics achieved with the configurationshown in FIG. 6, and the line C2 indicates the T-V characteristicsachieved with the configuration shown in FIG. 7. As shown in FIG. 8, inthe configuration shown in FIG. 7 in which protrusions are disposed atsmaller intervals, the threshold voltage is lower than that in theconfiguration shown in FIG. 6. Therefore, when both of theconfigurations shown in FIGS. 6 and 7 are provided in one pixel, areashaving different threshold voltages can be formed in the single pixel.Since the difference between the threshold voltages is 0.7 V or more,the viewing angle characteristics of the MVA-LCD can be significantlyimproved in the present mode for carrying out the invention.

Embodiment 1-1

A liquid crystal display according to Embodiment 1-1 in the present modefor carrying out the invention will be described with reference to FIGS.9 and 10. FIG. 9 shows the disposition of alignment regulatingstructures in one pixel of the liquid crystal display of the presentembodiment. As shown in FIG. 9, a plurality of gate bus lines 12 (two ofwhich are shown in FIG. 9) extending in the horizontal direction in thefigure are formed at intervals of, for example, 300 μm on a TFTsubstrate 2 of the liquid crystal display. A plurality of drain buslines 14 (two of which are shown in FIG. 9) extending in the verticaldirection in the figure are formed at intervals of, for example, 100 μmsuch that they intersect the gate bus lines 12 with an insulation film(not shown) interposed between them. A TFT 20 is formed in the vicinityof each of intersections between the gate bus lines 12 and the drain buslines 14. Storage capacitor bus lines 18 are formed such that theyextend across rectangular pixel regions defined by the gate bus lines 12and the drain bus lines 14 substantially in the middle of the regions. Apixel electrode 16 is formed at each of the pixel regions.

Linear protrusions 44 extending diagonally relative to edges of thepixel regions are formed on the TFT substrate 2. The protrusions 44 areformed by applying a resist on the entire surface of the substrate toform a resist layer and by patterning the resist layer using aphotolithographic process.

A color filter resin layer and a common electrode are formed on anopposite substrate 4 which is provided opposite to the TFT substrate 2.Protrusions 45 are formed on the opposite substrate 4, the protrusions45 being disposed in parallel with the protrusions 44 and with an offsetfrom the same by half a pitch. The protrusions 45 are formed by applyinga resist on the entire surface of the substrate to form a resist layerand by patterning the resist layer using a photolithographic process.

Intervals a2 between the protrusions 44 and 45 in top left and bottomleft areas of the pixel region are smaller than intervals a1 between theprotrusions 44 and 45 in the rest of the pixel region. Thus, areashaving different threshold voltages are both present in one pixel.

Although not shown, vertical alignment films are formed on surfaces ofthe substrate 2 and 4 opposite to each other. A nematic liquid crystalhaving negative dielectric anisotropy is sealed between the substrates 2and 4 which are combined together with spacers interposed between them.Polarizers are respectively applied to surfaces of the substrates 2 and4 constituting the exterior of the panel, the polarizers being disposedsuch that their absorption axes are orthogonal to each other.

Embodiment 1-2

FIG. 10 shows Embodiment 1-2 of a liquid crystal display in the presentmode for carrying out the invention. As shown in FIG. 10, a point-likeprotrusion 45′ and a frame-like protrusion 44 disposed to surround theprotrusion 45′ are formed in each of top left and bottom left areas of apixel region. Intervals a2 between the protrusions 44 and 45′ in thoseareas are smaller than intervals a1 between the protrusions 44 and 45 inthe rest of the pixel region. Thus, areas having different thresholdvoltages are both present in one pixel.

Embodiment 1-3

FIG. 11 shows the disposition of alignment regulating structures in onepixel of a liquid crystal display in the present mode for carrying outthe invention. As shown in FIG. 11, no linear protrusion as shown inFIG. 9 is formed on a TFT substrate 2, and slits 46 which are partialblanks in an electrode film of a pixel electrode 16 are formed instead.A plurality of slits 46′ having a space width smaller than that of theslits 46 are formed substantially orthogonally to directions in whichthe slits 46 extend, the series of protrusions 46′ being arranged in twoextending directions of the slits 46 that converge toward a storagecapacitor bus line 18 located in the middle of the pixel. An aligningdirection can be more reliably regulated by providing the slits 46′.

Linear protrusions 44 are formed on an opposite substrate 4 which isprovided opposite to the TFT substrate 2 and on which a color filterresin layer and a common electrode are formed, the linear protrusions 44being disposed in parallel with the slits 46 with an offset from thesame by half a pitch. The protrusions 44 are formed by applying a resiston the entire surface of the substrate to form a resist layer and bypatterning the resist layer using a photolithographic process.

Intervals a2 between the protrusions 44 and the slits 46 in top left andbottom left areas of the pixel region are smaller than intervals a1between the protrusions 44 and the slits 46 in the rest of the pixelregion. Thus, areas having different threshold voltages are both presentin one pixel.

As thus described, not only protrusions but also recesses or slitsformed on an electrode may be used as domain regulating units, and acombination of those features may alternatively be used. As shown inFIG. 11, patterns in the form of stripes may have a bent section, andthey may be accompanied by fine slits or fine protrusions for assistingdomain regulation along a part or whole of the same.

In the present mode for carrying out the invention, areas havingdifferent threshold voltages can be both provided in one pixel. Sincethis prevents a displayed image from appearing whitish in an obliquedirection, an MVA type liquid crystal display having high viewing anglecharacteristics can be provided.

Second Mode for Carrying Out the Invention

A liquid crystal display and a method of manufacturing the same in asecond mode for carrying out the invention will now be described withreference to FIGS. 12 to 27. In a Japanese patent application (numbered2002-52303) by the present applicant, a technique is proposed in which aphoto-setting composition mixed in a liquid crystal is set with adifferent pre-tilt angle in part of one pixel, as a technique forsolving the problem that a display image displayed in halftones appearswhitish in an oblique direction. According to this technique, areashaving different T-V characteristics such as threshold voltages can beformed in one pixel to improve gradation/viewing angle characteristics.

However, in order to vary T-V characteristics in one pixel, the pre-tiltangle of liquid crystal molecules must be increased at least in part ofthe pixel. A problem has thus arisen in that leakage of light is likelyto occur to result in a reduced contrast ratio at the time of full blackdisplay. In order to obtain different pre-tilt angles, it has beennecessary to apply voltages at a plurality of levels to the liquidcrystal layer in setting a photo-setting composition by irradiating itwith light. Further, a high optical irradiation energy is required toensure the pre-tilt of liquid crystal molecules. It is therefore desiredto improve production tact at steps for manufacturing liquid crystaldisplays.

It is an object of the present mode for carrying out the invention toprovide a liquid crystal display which can achieve high viewing anglecharacteristics and which can be manufactured with simple manufacturingsteps and to provide a method of manufacturing the same.

A principle behind the present mode for carrying out the invention willnow be described. FIG. 12 is a sectional view of a region substantiallyequivalent to one pixel showing a configuration of a liquid crystaldisplay in the present mode for carrying out the invention. As shown inFIG. 12, a pixel region is divided in areas A and B which are differentfrom each other in T-V characteristics. FIG. 13 is a graph showing T-Vcharacteristics in each of the areas. The abscissa axis representsvoltages applied to the liquid crystal, and the ordinate axis representslight transmittances. The line D1 in the graph indicates T-Vcharacteristics in the area A, and the line D2 indicates T-Vcharacteristics in the area B. The line D3 indicates composite T-Vcharacteristics obtained in the pixel as a whole including the areas Aand B. As already described, high viewing angle characteristics can beachieved by providing both of the areas A and B having different T-Vcharacteristics in one pixel.

FIG. 14 is a sectional view of a region substantially equivalent to onepixel showing another configuration of a liquid crystal display in thepresent mode for carrying out the invention. The same effect can beachieved when each of the areas A and B is divided into a plurality ofparts as shown in FIG. 14. Alternatively, a pixel region may be dividedinto three or more regions A, B, C, and so on which are different fromeach other in T-V characteristics.

A method of manufacturing a liquid crystal display in the present modefor carrying out the invention will now be described in comparison tothe related art. FIGS. 15A to 15F are sectional views taken in processesshowing a method of manufacturing a liquid crystal display according tothe related art. First, transparent electrodes and so on are formed on aglass substrate (or plastic substrate) to fabricate a TFT substrate 2(or opposite substrate 4) as shown in FIG. 15A. Next, as shown in FIG.15B, a printing process is used to apply a polyimide resin to the TFTsubstrate 2 and is baked at a high temperature to form an alignment film36. The baking at a high temperature may not be performed when a plasticsubstrate is used, and a resin that is baked at a low temperature isfrequently used as the material to form the alignment film 36 in suchcases. Rubbing is then performed using a rubbing roller 38 as shown inFIG. 15C if necessary.

Next, as shown in FIG. 15D, an opposite substrate 4 on which analignment film 36 has been formed at similar steps is combined with theTFT substrate 2 with a seal material 62 interposed between them. Next,as shown in FIG. 15E, a liquid crystal 6 is injected through a liquidcrystal injection hole and is sealed to complete a liquid crystaldisplay as shown in FIG. 15F.

FIGS. 16A to 16C are sectional views taken in processes showing a methodof manufacturing a liquid crystal display in the present mode forcarrying out the invention. First, as shown in FIG. 16A, a TFT substrate2 and an opposite substrate 4 having no alignment film 36 formed thereonare combined together with a sealing material (not shown) interposedbetween them. Next, as shown in FIG. 16B, a liquid crystal 6 mixed witha photo-setting resin which is an alignment assisting material isinjected between the substrates 2 and 4. The liquid crystal 6 is thenirradiated with light to set the photo-setting resin in the vicinity ofthe substrates 2 and 4, thereby forming alignment controlling layers 34as shown in FIG. 16C. No voltage is applied to the liquid crystal 6 atthe step of irradiating the liquid crystal 6 with light.

FIGS. 17A to 17C are sectional views showing the flow of the formationof the alignment controlling layers 34. As shown in FIGS. 17A and 17B,the photo-setting resin (monomers) M in the liquid crystal 6 at aninterface with the substrate 2 is polymerized into a polymer P1 whenirradiated with UV light. When irradiation with UV light is furthercontinued, as shown in FIG. 17C, polymers P2 are formed which arealigned perpendicularly to the polymer P1 at the interface with thesubstrate, and the polymers P1 and P2 function as a vertical alignmentcontrolling layer to align liquid crystal molecules 8 vertically.

The method of manufacturing a liquid crystal display in the present modefor carrying out the invention is characterized in that the alignmentfilm 36 is not formed on the substrates 2 and 4 or is formed only inpart of a pixel region unlike the method of manufacturing a liquidcrystal display according to the related art. The alignment of theliquid crystal 6 is controlled by the alignment controlling layers 34.When no alignment film 36 is formed, a liquid crystal display can befabricated without steps which involve heating of the substrates at ahigh temperature including the step for forming the alignmentcontrolling layers 34. Since this allows plastic substrates or very thinglass substrates to be used as the TFT substrate 2 and the oppositesubstrate 4, freedom in selecting substrates is increased. In thepresent mode for carrying out the invention, no voltage is applied tothe liquid crystal 6 when the alignment controlling layers 34 areformed. Thus, steps for manufacturing the liquid crystal display aresimplified.

According to the above-described techniques in the related art,different T-V characteristics are achieved in one pixel primarily byvarying the tilting angle of liquid crystal molecules relative to thesubstrates. On the contrary, in the present mode of carrying out theinvention, liquid crystal molecules are tilted at the same angle in onepixel, and different T-V characteristics are achieved in one pixelutilizing a difference between anchoring energies applied by alignmentcontrolling layers 34 to liquid crystal molecules. A continued studyrevealed that it is difficult to utilize a difference between anchoringenergies in a liquid crystal display panel assembled after formingvertical alignment films because the anchoring energies become too high.In the present mode for carrying out the invention, however, since novertical alignment film is formed (or formed only in part of a pixelregion), a liquid crystal display panel having small anchoring energiescan be fabricated. It is therefore easy to provide different anchoringenergies in a pixel.

In the present mode for carrying out the invention, since liquid crystalmolecules are not required to have a great pre-tilt angle, leakage oflight can be avoided when black is displayed. This makes it possible toprovide a liquid crystal display having improved gradation/viewing anglecharacteristics and a high contrast ratio.

FIGS. 18A and 18B show a method of forming alignment controlling layers34 having different anchoring energies in one pixel. First, as shown inFIG. 18A, an area A of one pixel of a liquid crystal panel formed byinjecting a liquid crystal 6 mixed with a photo-setting resin betweensubstrates 2 and 4 is irradiated with, for example, a predetermined doseof UV light using an exposure mask 54. Next, as shown in FIG. 18B, anarea B of the same pixel is irradiated with UV light in a dose differentfrom that mentioned above using an exposure mask 55 formed with ashielding pattern that is complementary to the exposure mask 54. Byirradiating the area A and the area B in the single pixel with UV lightin different doses, alignment controlling layers 34 having differentanchoring energies are formed in the areas A and B. Therefore, differentT-V characteristics (threshold voltages) can be achieved in the areas Aand B in the single pixel.

FIG. 19 shows another example of a method of forming alignmentcontrolling layers 34 having different anchoring energies in one pixel.As shown in FIG. 19, an exposure mask 56 whose transmittance variesdepending on areas is used to irradiate areas A and B in one pixel withUV light having different irradiation intensities. According to thismethod, since alignment controlling layers 34 having different anchoringenergies are obtained through full plate exposure, manufacturing stepsare further simplified.

FIG. 20 shows still another example of a method of forming alignmentcontrolling layers 34 having different anchoring energies in one pixel.As shown in FIG. 20, an optical band-pass filter 58 is used to vary thewavelength of UV light that enters a liquid crystal 6. It is alsoadvantageous to use a plurality of band-pass filters 58 at the time ofirradiation with UV light. For example, a predetermined band-pass filter58 is used for irradiation with UV light up to a certain phase ofirradiation; another band-pass filter 58 is used for irradiation with UVlight up to a certain subsequent phase of irradiation; and irradiationwith UV light is thereafter performed using no band-pass filter 58.

FIG. 21 is a graph showing dependence of a T-V curve on the dose ofirradiation with light (total energy). The line E1 represents a T-Vcurve resulting from a UV irradiation dose of 0.2 J (a small UVirradiation dose). The line E2 represents a T-V curve resulting from aUV irradiation dose of 0.6 J (a medium UV irradiation dose). The line E3represents a T-V curve resulting from a UV irradiation dose of 3 J (alarge UV irradiation dose). As shown in FIG. 21, liquid crystalmolecules stand up earlier when the dose of UV irradiation is smallbecause the anchoring energies of the alignment controlling layers 34are small. The anchoring energies of the alignment controlling layers 34increase with the dose of UV irradiation, and the T-V curve is shiftedtoward a high voltage side.

In this example, no optical initiator (polymerization initiator) is usedin the photo-setting resin in the mixed liquid crystal. Since no opticalinitiator is used, an anchoring energy difference can be more easilymade available. FIG. 22 is a graph showing dependence of T-Vcharacteristics on the dose of irradiation with light in a case whereinan optical initiator is used. The line F1 represents a T-V curveresulting from a UV irradiation dose of 0.2 J (a small UV irradiationdose). The line F2 represents a T-V curve resulting from a UVirradiation dose of 0.6 J (a medium UV irradiation dose). The line F3represents a T-V curve resulting from a UV irradiation dose of 3 J (alarge UV irradiation dose). The optical initiator is added such that itis about 2 to 10%, by weight, of the total amount of a monofunctionalmonomer and a bifunctional monomer. A comparison between FIGS. 22 and 21indicates that differences between the T-V curves depending on thedifferent doses of UV irradiation are small when an optical initiator isused. It is therefore preferable to use no optical initiator in order tomake an anchoring energy difference available.

FIGS. 23 to 26 show sectional configurations of a liquid crystal displayfabricated according to the method of manufacturing a liquid crystaldisplay in the present mode for carrying out the invention. As shown inFIG. 23, alignment controlling layers 34 having a predeterminedanchoring energy are formed in an area A of a pixel region. In an areaB, alignment controlling layers 34′ having an anchoring energy differentfrom that in the area A are formed.

The alignment controlling layers 34 and 34′ may alternatively be formedafter forming underlying layers 40 on substrates 2 and 4 as shown inFIG. 24. For example, the underlying layers 40 are partiallypre-processed such that they have different degrees of surface activityto make the alignment controlling layers 34 and 34′ definitely differentfrom each other, thereby providing a great difference between theiranchoring energies.

As shown in FIG. 25, vertical alignment films 36 may be formed as theunderlying layers. For example, the vertical alignment films 36 arepatterned such that the alignment controlling layers 34 are selectivelyformed in the area A in which the vertical alignment films 36 areremoved and such that vertical alignment films 36 are used as they arein the region B without forming the alignment controlling layers 34.

It is also advantageous to use the present mode for carrying out theinvention for substrates having an irregular section 48 on a surfacethereof, as shown in FIG. 26. Specifically, since irregular sections 48formed on substrates 2 and 4 are leveled by, for example, a CF resinlayer or linear protrusions, there is no need for providing a levelinglayer. This simplifies manufacturing steps and reduces manufacturingcosts. In the case of a reflective liquid crystal display, alignmentcontrolling layers 34 may be directly formed on a surface of areflective electrode having a tilt angle. Although it is sometimesdifficult to form an alignment film 36 on a substrate having anirregular section 48 on a surface thereof or a substrate used in areflective liquid crystal display using a printing process, an alignmentcontrolling layer 34 can be uniformly formed in the present mode forcarrying the invention.

FIG. 27 is a graph showing T-V characteristics in an area havingalignment controlling layers 34 formed therein of a liquid crystaldisplay panel having a configuration as shown in FIG. 6 and showing T-Vcharacteristics in an area having vertical alignment films 36 formedtherein of the same panel. The line G1 indicates the T-V characteristicsin the area having the alignment controlling layers 34 formed therein,and the line G2 indicates the T-V characteristics in the area having thevertical alignment films 36 formed therein. As shown in FIG. 27, ananchoring energy and a threshold voltage in the area having thealignment controlling layers 34 formed therein are smaller than those inthe area having the vertical alignment films 36 formed therein. It iseasier to provide different anchoring energies in a pixel, in a liquidcrystal display panel formed with alignment controlling layers 34 and novertical alignment film 36 or a liquid crystal display panel havingalignment controlling layers 34 formed in areas in which verticalalignment films 36 have been removed through patterning, than in aliquid crystal display panel having vertical alignment films 36 formedon entire surfaces thereof.

The description will now be continued with reference to specificembodiments.

Embodiment 2-1

Each of a pair of glass substrates having a transparent electrodeconstituted by an ITO patterned thereon was cleaned. Bead spacers havinga diameter of 4.0 μm (manufactured by Fine Chemicals Division, SekisuiChemical Co., Ltd.) were dispersed on either of the substrates, and athermosetting seal (manufactured by Mitsui Chemicals, Inc) was appliedto the other substrate with a dispenser. The substrates were thencombined to fabricate an open cell. A liquid crystal (manufactured byMerck and having Δ∈=−4.8) and a resin were mixed in a weight ratio of98:2. The resin was a mixture of a monofunctional monomer (dodecylacrylate manufactured by Wako Pure Chemical Industries, Ltd.) and abifunctional monomer (manufactured by Merck) in a weight ratio of 15:1.The mixed liquid crystal thus prepared was charged in the open cellusing vacuum injection, and the injection hole was thereafter sealedwith a visible-light-setting resin to fabricate a liquid crystal cell.The liquid crystal cell was irradiated with UV light having an intensityof 1 mW/cm². At this time, an area A was formed by irradiating it withUV light having a dose 0.2 J using an exposure mask 54 for shielding anarea B from light, and the area B was formed by irradiating it with UVlight having a dose of 3 J using an exposure mask 55 for shielding thearea A from light. Thus, a liquid crystal panel was fabricated which haddifferent T-V characteristics in a pixel depending on locations. Each ofthe areas A and B was formed like stripes having a width of 20 μm.Measurement of T-V characteristics using a λ/4 plate revealed that therewas a significant improvement of gradation/viewing anglecharacteristics.

Embodiment 2-2

Open cells and a mixed liquid crystal similar to those in Embodiment 2-1were used to fabricate three types of liquid crystal panels. The liquidcrystal panels were irradiated with UV light in three different doses(0.2 J, 0.6 J and 3 J) without using the exposure masks 54 and 55. As aresult of measurement of T-V characteristics performed in the same wayas in Embodiment 2-1, it was observed that the liquid crystal panels haddifferent T-V characteristics as shown in the graph of FIG. 21.

Embodiment 2-3

Liquid crystal panels were fabricated under the same conditions as thosein Embodiment 2-2 except that a polymerization initiator was mixed inthe mixed liquid crystal. The polymerization initiator used was Irgacure651 (manufactured by Ciba Specialty Chemicals Holding Inc.). A smallamount of the polymerization initiator was added to reach 2.5% by weightof the amount of the monofunctional monomer and the bifunctional monomerthat were mixed. Three types of liquid crystal panels were fabricated byusing three different doses of irradiation (0.2 J, 0.6 J and 3 J) justas done in Embodiment 2-2. Measurement of T-V characteristics of theliquid crystal panels revealed that it was difficult to provide theliquid crystal panels with different T-V characteristics as in the graphshown in FIG. 22 and that it was preferable to add no polymerizationinitiator.

Third Mode for Carrying Out the Invention

A liquid crystal display and a method of manufacturing the same in athird mode for carrying out the invention will now be described withreference to FIGS. 28 to 36. MVA mode and In-Plane Switching (IPS) modedisplays are well known as liquid crystal displays which have highdisplay quality and, in particular, high viewing angle characteristics.

FIG. 28 shows a schematic sectional configuration of an MVA-LCD. Asshown in FIG. 28, the MVA-LCD has a TFT substrate 2, an oppositesubstrate 4, and a liquid crystal 6 sealed between the substrates 2 and4. The liquid crystal 6 has negative dielectric constant anisotropy. Forexample, a linear protrusion 44 as an alignment regulating structure isformed on the TFT substrate 2. Although not shown, vertical alignmentfilms are formed on surfaces of the substrates 2 and 4 opposite to eachother. When no voltage is applied to the liquid crystal 6, liquidcrystal molecules 8 in the vicinity of the protrusion 44 are tiltedtoward directions normal to inclined surfaces of the protrusion 44 froma direction perpendicular to the substrate surfaces. By applying apredetermined voltage to the liquid crystal 6, the liquid crystalmolecules 8 are tilted in different directions, the protrusion 44serving as a boundary between the tilts. The MVA LCD has high viewingangle characteristics because the tilting direction of the liquidcrystal molecules 8 is divided into, for example, four directions in onepixel.

FIG. 29 shows a schematic sectional configuration of an IPS mode liquidcrystal display. As shown in FIG. 29, in the IPS mode liquid crystaldisplay, a predetermined voltage is applied between pixel electrodes 16formed like comb-teeth on a TFT substrate 2 to switch liquid crystalmolecules 8 by the action of a horizontal electric field in parallelwith the substrate. The IPS mode liquid crystal display has high viewingangle characteristics because the liquid crystal molecules 8 are alwayssubstantially in parallel with the substrates.

However, those liquid crystal displays still have problems. For example,the viewing angle characteristics of an MVA-LCD become insufficient atthe time of a gradation change. In the case of an IPS mode liquidcrystal display, sufficiently high contrast cannot be achieved in adirection square to the same. An MVA-CLD has problems withgradation/viewing angle characteristics including the problem that animage displayed in halftones appears whitish in an oblique direction orappears with different tints when viewed in oblique and squaredirections. On the contrary, in the IPS mode, contrast in a squaredirection is limited to about 200 to 300 because of the horizontalalignment. Contrast in an oblique direction at an angle of 45° is notsufficient compared to that of an MVA-LCD. Improvement of transmittanceis also desired. There is another problem that undesirable coloringoccurs when black display is viewed in an oblique direction. As thusdescribed, even liquid crystal displays in the above-described excellentoperation modes have merits and demerits, and further improvements aredesired for them.

The present mode for carrying out the invention is aimed at improvinggradation/viewing angle characteristics which are a problem of verticalalignment type liquid crystal displays in particular. Besides theabove-described display methods, the halftone-grayscale method is knownas a technique for improving viewing angle characteristics. According tothe halftone-grayscale method, viewing angle characteristics areimproved by varying a threshold voltage for a liquid crystal in onepixel to provide a mixture of different T-V characteristics. Oneapproach to this is a technique in which different voltages are appliedto a liquid crystal utilizing capacitive coupling. However, a problemhas arisen in that steps for manufacturing a liquid crystal displaybecome complicated and in that the structure of a liquid crystal displaybecomes complicated. In the present mode for carrying out the invention,a threshold voltage is easily controlled in a pixel of a verticalalignment type liquid crystal display to achieve a significantimprovement of gradation/viewing angle characteristics consequently.

First, a principle behind the present mode for carrying out theinvention will be described. FIG. 30 is a sectional view of a regionsubstantially equivalent to one pixel showing a configuration of aliquid crystal display in the present mode for carrying out theinvention. As shown in FIG. 30, a certain area of the pixel has a cellthickness smaller than that in the rest of the pixel. It is known thatthe response time of a liquid crystal is inversely proportionate to thesquare of the cell thickness in general. Specifically, the time of aresponse to the application of voltage is relatively short in the regionhaving the smaller cell thickness, and the time of a response to theapplication of the voltage is relatively long in the other region havingthe greater cell thickness. In the present mode for carrying out theinvention, this phenomenon is used to provide a different pre-tilt anglein part of a pixel. The liquid crystal 6 used is added with a reactivemonomer.

A voltage that is a repetition of an off-voltage (for displaying blackin a vertical alignment type normally black mode) and an on-voltage (fordisplaying white in the vertical alignment type normally black mode) isapplied between a pixel electrode 16 (not shown) on a TFT substrate 2and a common electrode 42 on an opposite substrate 4, the voltage beingapplied at a frequency appropriately selected based on the speed ofresponse of the liquid crystal. The off-voltage is a voltage whichcauses no change in the alignment of liquid crystal molecules 8. Theon-voltage is a voltage that is sufficient to provide the molecules witha pre-tilt angle. The frequency is basically set such that the liquidcrystal will respond in the area of quick response and will not respondin the area of slow response at that frequency. It should be noted thatthe “on-voltage” and “off-voltage” are not necessarily voltages at whichthe liquid crystal display panel is actually driven. The voltages arechosen such that a pre-tilt angle is provided (or a threshold voltagechanges) as a result of polymerization and solidification of a monomer,and values higher than an actual driving voltage are used in general. Anacrylate type or methacrylate type monomer which is polymerized whenirradiated with UV light is used as the monomer. The monomer ispolymerized and solidified when it is irradiated with UV light with avoltage applied thereto.

FIG. 31 is a sectional view of a region substantially equivalent to onepixel showing a pre-tilt angle of liquid crystal molecules of the liquidcrystal display in the present mode for carrying out the invention. Asshown in FIG. 31, the pre-tilt angle of liquid crystal molecules 8′changes (from 90° to about)85°) in an area of quick response in part ofthe pixel, and the pre-tilt angle of liquid crystal molecules 8 inanother area of slow response undergoes substantially no change (orstays at about)90°).

FIG. 32 is a graph showing T-V characteristics of the liquid crystaldisplay in the present mode for carrying out the invention. The line H1indicates T-V characteristics of the area in which the pre-tilt anglehas not changed, and the line H2 indicates T-V characteristics of thearea in which the pre-tilt angle has changed. The line H3 indicatescomposite T-V characteristics obtained throughout the pixel. As shown inFIG. 32, the threshold voltage is decreased resulting in a change in T-Vcharacteristics in the area where the pre-tilt angle has changed.Gradation/viewing angle characteristics of the pixel as a whole areimproved because the T-V characteristics of those areas are combined.

In the present mode for carrying out the invention, areas havingdifferent speeds of response are formed in a pixel, and a drivingvoltage and frequency for polymerizing and solidifying a reactivemonomer are chosen based on the response speeds of the liquid crystal,which makes it possible to provide a different pre-tilt angle in part ofthe pixel. The threshold voltage of the liquid crystal can be varied inthe pixel by providing a different pre-tilt angle in a part thereof,which consequently makes it possible to improve gradation/viewing anglecharacteristics. In the present mode for carrying out the invention, itis possible to significantly improve gradation/viewing anglecharacteristics which have been an important problem of verticalalignment type liquid crystal displays using a simple method.

The description will now be continued with reference to specificembodiments.

Embodiment 3-1

A description will now be made on a liquid crystal display and a methodof manufacturing the same according to Embodiment 3-1 in the presentmode for carrying the invention. FIG. 33 is a sectional view of a regionsubstantially equivalent to one pixel showing a configuration of theliquid crystal display of the present embodiment. As shown in FIG. 33,one pixel is divided into an area A having a cell thickness d1 and anarea B having a cell thickness d2 (<d1), and a pre-tilt angle isefficiently achieved in the area B in which a liquid crystal 6 respondsquickly. The liquid crystal 6 has negative dielectric constantanisotropy (Δ∈=−3.5). Polyamic acid type vertical alignment films areused. A bifunctional acrylate or methacrylate having a liquid crystalskeleton was used as a reactive monomer to be mixed. The amount of thereactive monomer mixed in the liquid crystal was 0.4% by weight. Thecell thickness d1 was about 4 μm, and the cell thickness d2 was 2 μm. Astep was formed on a surface of a substrate by patterning a resinprotective film 60 having a thickness of 2 μm.

FIG. 34 is a graph showing how a voltage applied to the liquid crystal 6of the present embodiment changes with time. A low voltage V1 was 0 V,and a high voltage V2 was 4 V. Times t1 and t2 were both 8 ms. Theliquid crystal was irradiated with UV light of 10 J/cm² (equivalent to aUV 35 filter) while applying the voltage under such conditions. When themonomer in the liquid crystal is polymerized and solidified under suchconditions, a polymer chain is formed in the area B at the interfacebetween the area and the alignment film because the liquid crystalresponds quickly in the area, the polymer chain following liquid crystalmolecules which have been tilted. Thus, the liquid crystal molecules canbe provided with a pre-tilt angle of 90° or less. On the contrary, inthe area A, the liquid crystal responds more slowly because of thegreater cell thickness, and substantially no tilt of liquid crystalmolecules occurs in the area under the above-described conditions.Therefore, even if the monomer is solidified in this state, it will notimpart a pre-tilt angle of 90° or less to liquid crystal molecules inthat area because a polymer chain is formed such that it follows theliquid crystal molecules which are kept aligned vertically.

It is therefore possible to vary the threshold voltage for the liquidcrystal between the areas A and B by varying the pre-tilt angle in thesingle pixel as thus described. That is, the threshold voltage in thearea B is lower than that in the area A. Measurement of the thresholdvoltages in the two areas A and B revealed that there was a differenceof about 0.5 V. The threshold voltages could be thus controlled using arelatively simple method as described above to improve gradation/viewingangle characteristics consequently.

The effect of improving viewing angle characteristics was observed whenthe area ratio between the areas B and A was about 1:10. A preferablearea ratio depends on the difference between the threshold voltages. Anexperiment (observation of display) and a simulation have revealed thatan area ratio in the range from 1:10 to 1:1 is preferable when thethreshold voltage difference is in the range from 0.3 V to 1 V.

Embodiment 3-2

A method of manufacturing a liquid crystal display according toEmbodiment 3-2 in the present mode for carrying out the invention willnow be described. The present embodiment is an example of theapplication of the present mode for carrying out the invention to aliquid crystal display having areas with a different initial pre-tiltangle in some parts thereof. An initial pre-tilt angle is a pre-tiltangle which is present before a polymer is solidified. FIG. 35 shows asectional configuration of a liquid crystal display which has areas witha different initial pre-tilt angle in some parts thereof. In FIG. 35,alignment films are omitted from illustration. As shown in FIG. 35,linear protrusions (banks having low dielectric properties) 44 and 45are formed on substrates 2 and 4, respectively. Thus, liquid crystalmolecules in the vicinity of the protrusions 44 and 45 are provided witha predetermined initial pre-tilt angle. A voltage which changes withtime as shown in FIG. 34 during polymerization of a monomer is appliedto a liquid crystal 6 in the liquid crystal display having such aconfiguration, and this makes it possible to achieve a partial pre-tiltangle more efficiently. Specifically, the liquid crystal 6 whichincludes a polymeric monomer is irradiated with UV light while drivingit in a way similar to the cyclic reset driving method, which makes itpossible to efficiently provide a pre-tilt angle only in areas B wherethe liquid crystal 6 responds quickly. Polymerizing and drivingconditions are substantially the same as those in Embodiment 3-1.

In the case of static driving that is commonly used, it is not possibleto introduce great differences between pre-tilt angles of liquid crystalmolecules at substrate interfaces in respective areas when there is notso great variation in the initial alignment of the liquid crystalmolecules. Therefore, a sufficient threshold voltage difference cannotbe provided even if a polymeric monomer is used. However, when drivingsimilar to the cyclic reset driving method is used as in the presentembodiment, a slight difference in initial alignment of liquid crystalmolecules can be enlarged. By solidifying the polymeric monomer andfixing it at substrate interfaces in this state, an area having agreater threshold voltage difference (an area in which the pre-tiltangle becomes greater) can be consequently formed in one pixel.Therefore, the gradation/viewing angle characteristics of the liquidcrystal display can be improved. Although an oblique electric field mustbe taken into consideration when the alignment of liquid crystalmolecules in the vicinity of the protrusions 44 and 45 is discussed, thedescription has been focused on the initial pre-tilt angle only in orderto avoid complicatedness.

The impartment of a pre-tilt by typical oblique electric fields will nowbe described. FIG. 36 shows a sectional configuration of a liquidcrystal display having slits formed therein. In FIG. 36, alignment filmsare omitted from illustration. As shown in FIG. 36, an electrode blanksection (slit) 46 is formed on each of substrates 2 and 4. When theapplied voltage is sufficiently low, the initial pre-tilt angle issubstantially 90° in the entire area. When a voltage is applied to aliquid crystal 6, oblique electric fields are generated in the vicinityof the slits 44, the electric fields being different in direction fromthose in other areas. Liquid crystal molecules in the vicinity of theslits 44 are first tilted by the oblique electric fields. When thevoltage is applied to the liquid crystal 6 using driving similar to thecyclic reset driving method as described above, the liquid crystalmolecules in the vicinity of the slits 44 are tilted more greatly thanthose in the other areas. Such alignment of liquid crystal molecules canbe fixed by solidifying a polymeric monomer in this state. Polymerizingconditions and driving conditions are basically the same as those inEmbodiment 1-1. According to the present embodiment, a liquid crystaldisplay can be consequently fabricated with a structure which has apre-tilt angle difference in a part thereof, and a definite thresholdvoltage difference is produced between an area B and another area A inthe vicinity of the slits 46.

As described above, in the present mode for carrying out the invention,a definite threshold voltage difference can be produced in one pixel bymaking use of a difference between response speeds of a liquid crystal,a polymeric monomer, and driving similar to the cyclic reset drivingmethod. It is therefore possible to provide a vertical alignment typeliquid crystal display having high gradation/viewing anglecharacteristics.

Fourth Mode for Carrying Out the Invention

The present mode for carrying out the invention relates to a liquidcrystal display used as a display section of a television receiver or anelectronic apparatus and a method of manufacturing the same, moreparticularly, to a liquid crystal display in which a monomer or oligomeradded in a liquid crystal is polymerized and a method of manufacturingthe same.

A liquid crystal display has two substrates and a liquid crystal sealedbetween the substrates. In a liquid crystal display, optical switchingis caused by electrical stimuli utilizing electro-optical anisotropy ofa liquid crystal. A predetermined voltage is applied to a liquid crystallayer to control the tilting angle of liquid crystal molecules, therebychanging the direction of the axis of anisotropy of the refractivity ofthe liquid crystal molecules. Resultant optical rotation andbirefringence are utilized to change light transmittance, and theluminance of each pixel of a liquid crystal display panel is therebycontrolled. The vertical aligned (VA) mode is one of techniques for sucha liquid crystal display panel. The VA mode has been put in practicaluse as an operation mode in which a wide viewing angle can be achieved,as typically experienced in an MVA (Multi-domain Vertical Alignment)type liquid crystal display (hereinafter referred to as “MVA-LCD”).

In a VA mode liquid crystal display, however, a problem arises in that adisplayed image in halftones appears whitish when viewed in a directionoblique to the display screen. As a method for solving this, a Japanesepatent application (numbered 2002-52303) made by the present applicanthas proposed a technique in which a plurality of areas having differentpre-tilt angles of liquid crystal molecules are formed in one pixel toform areas having different rising voltages of T-V characteristics inthe single pixel.

In a Japanese patent application (numbered 2001-98455) made by thepresent applicant, a technique as described below is proposed as atechnique for providing a pre-tilt angle. A pre-tilt of liquid crystalmolecules can be achieved by adding a monomer or oligomer which isoptically or thermally reacted for polymerization in the liquid crystalin advance and by polymerizing the monomer or oligomer after the liquidcrystal is injected. The pre-tilt angle can be varied by varying avoltage that is applied to the liquid crystal at the time ofpolymerization. The pre-tilt angle becomes smaller, the higher theapplied voltage. A pre-tilt angle is an angle at which liquid crystalmolecules are tilted with respect to a substrate surface when no voltageis applied to the liquid crystal layer. That is, “a reduction in apre-tilt angle” means an increase in an angle of inclination fromperfect vertical alignment or approaching to horizontal alignment.

It is an object of the present mode for carrying out the invention toprovide a liquid crystal display which can achieve high displaycharacteristics and a method of manufacturing the same.

The above object is achieved by a liquid crystal display characterizedin that it has a pair of substrates provided opposite to each other, astorage capacitor bus line formed on either of the pair of substrates, aplurality of divisional areas which are a plurality of divisions of eachof pixel regions arranged on either of the pair of substrates, a pixelelectrode formed at each of the divisional areas, a thin film transistorformed at each of the divisional areas and connected to the pixelelectrode, a common electrode formed on the other of the pair ofsubstrates, a liquid crystal sealed between the pair of substrates, anda polymer obtained by polymerizing a polymeric component mixed in theliquid crystal while applying an AC voltage between the common electrodeand the storage capacitor bus line.

A liquid crystal display in the fourth mode for carrying out theinvention will be described with reference to FIGS. 39 to 49. First, adescription will be made on a technique that constitutes a base of thepresent mode for carrying out the invention. In Japanese patentapplications (numbered 2001-306906 and 2002-136128) made by the presentapplicant, a technique is disclosed in which an AC voltage is appliedbetween a common electrode and a storage capacitor bus line as a methodfor applying a voltage to a liquid crystal layer when polymerizing amonomer or oligomer.

FIG. 39 schematically shows a configuration of a liquid crystal displayin which the above-described technique is used. As shown in FIG. 39, aplurality of gate bus lines 112 extending in the horizontal direction inthe figure are formed in parallel with each other on a TFT substrate.One end of each gate bus line 112 is connected to a gate bus linedriving circuit 180 for driving the gate bus lines 112. A plurality ofdrain bus lines 114 extending in the vertical direction in the figureare formed in parallel with each other such that they intersect the gatebus lines 112 with an insulation film interposed between them. One endof each drain bus line 114 is connected to a drain bus line drivingcircuit 182 for driving the drain bus lines 114. A TFT 120 is formed inthe vicinity of each of intersections between the gate bus lines 112 andthe drain bus lines 114. A gate electrode of the TFT 120 is connected tothe gate bus line 112, and a drain electrode of the same is connected tothe drain bus line 114. A source electrode of the TFT is connected to apixel electrode 116, a pixel electrode 116 being formed at each pixel.

A plurality of storage capacitor bus lines 118 are formed in parallelwith the gate bus lines 112. A storage capacitor bus line 118constitutes one electrode of a storage capacitor at each pixel. One endof each storage capacitor bus line 118 is electrically connected to asingle common storage capacitor wiring 117. A common storage capacitorterminal 170 is provided at one end of the common storage capacitorwiring 117. A predetermined voltage Vcs can be applied to the commonstorage capacitor wiring 117 and the storage capacitor bus lines 118through the common storage capacitor terminal 170.

A common electrode 142 is formed substantially on an entire surface ofthe opposite electrode. The common electrode 142 constitutes oneelectrode of a liquid crystal capacitance at each pixel. A commonelectrode terminal 172 is connected to the common electrode 142. Apredetermined voltage Vc can be applied to the common electrode 142through the common electrode terminal 172. The common storage capacitorwiring 117 and the common electrode 142 may be electrically connectedafter a step for polymerizing a monomer or oligomer to form a polymer.

FIG. 40 shows a schematic sectional configuration of a liquid crystaldisplay panel. As shown in FIG. 40, a liquid crystal 106 is sealedbetween a TFT substrate 102 and an opposite substrate 104 which arecombined in a face-to-face relationship. TFTs 120, pixel electrodes 116and a vertical alignment film 134 are formed on a glass substrate 110constituting the TFT substrate 102. Color filter (CF) resin layers 133,a common electrode 142 and an alignment film 135 are formed on a glasssubstrate 111 constituting the opposite substrate 104. A cell gap ismaintained between the substrates 102 and 104 by spherical spacers 140dispersed on the TFT substrate 102 or opposite substrate 104.

When light (UV light) is radiated in the direction of the thick arrow inFIG. 40 with a voltage applied to the liquid crystal 106, a monomer oroligomer added in the liquid crystal 106 is polymerized to form apolymer. Thus, a predetermined pre-tilt angle is obtained as an initialstate of alignment of liquid crystal molecules. The pre-tilt angle issmaller, the higher the voltage applied to the liquid crystal 106 whenthe polymer is formed.

When an AC voltage is applied between the common electrode 142 andstorage capacitor bus lines 118, a circuit is formed at each pixel, thecircuit comprising a liquid crystal capacitance Clc and a storagecapacitor Cs which are coupled in series and across which the AC voltageis applied. The voltage applied to the liquid crystal 106 when apredetermined AC voltage is applied is expressed by the followingequation where Zlc represents the impedance of the liquid crystalcapacitance Clc, and Zc represents the impedance of the storagecapacitor Cs.Voltage Applied to Liquid Crystal=Zlc/(Zlc+Zc)×AC voltage  (Equation 1)

Next, the liquid crystal display in the present mode for carrying outthe invention will be described with reference to FIG. 41. In order toensure that areas having different pre-tilt angles of liquid crystalmolecules will be formed in one pixel, a different voltage must beapplied to each of the areas when the monomer or oligomer mixed in theliquid crystal 106 is polymerized. In the present mode for carrying outthe invention, a plurality of pixel electrodes electrically insulatedfrom each other or a plurality of pixel electrodes connected to eachother through high resistance are formed in one pixel. For example, aplurality of pixel electrodes and a plurality of TFTs connected to theplurality of pixel electrodes, respectively, are formed in one pixel.Areas in which the pixel electrodes are formed are divisional areaswhich are a plurality of divisions of the pixel region.

When the liquid crystal 106 is irradiated with UV light, an AC voltageis applied between the common electrode 142 and the storage capacitorbus lines 118. At this time, the voltage applied to the liquid crystal106 in each of the divisional areas is determined by the liquid crystalcapacitance Clc and the storage capacitor Cs as indicated by Equation 1.As a result, a plurality of different voltages can be applied to theliquid crystal 106 in one pixel.

FIG. 41 shows an equivalent circuit of one pixel of the liquid crystaldisplay, three divisional areas being formed in the single pixel. Asshown in FIG. 41, the single pixel is divided into three divisionalareas α, β and γ. The divisional area α has a liquid crystal capacitanceClc1 and a storage capacitor Cs1 which are connected in series. Thedivisional area β has a liquid crystal capacitance Clc2 and a storagecapacitor Cs2 which are connected in series. The divisional area γ has aliquid crystal capacitance Clc3 and a storage capacitor Cs3 which areconnected in series.

The common electrode 142 constitutes one electrode of each of the liquidcrystal capacitances Clc1 to Clc3. A first pixel electrode formed at thedivisional area α constitutes another electrode of the liquid crystalcapacitance Clc1 and constitutes one electrode of the storage capacitorCs1. A second pixel electrode formed at the divisional area βconstitutes another electrode of the liquid crystal capacitance Clc2 andconstitutes one electrode of the storage capacitor Cs2. A third pixelelectrode formed at the divisional area γ constitutes another electrodeof the liquid crystal capacitance Clc3 and constitutes one electrode ofthe storage capacitor Cs3. The storage capacitor bus line 118constitutes another electrode of each of the storage capacitors Cs1 toCs3. The pairs of the liquid crystal capacitance Clc1 and the storagecapacitor Cs1, the liquid crystal capacitance Clc2 and the storagecapacitor Cs2, and the liquid crystal capacitance Clc3 and the storagecapacitor Cs3 are parallel-connected to each other.

When the monomer or oligomer mixed in the liquid crystal 106 ispolymerized to form a polymer, the liquid crystal 106 is irradiatedwith, for example, UV light while applying an AC voltage between thecommon electrode 142 and the storage capacitor bus lines 118 by an ACpower source 174.

Although not shown, a source electrode of a first TFT is connected to aconnection point A; a source electrode of a second TFT is connected to aconnection point B; and a source electrode of a third TFT is connectedto a connection point C. Gate electrodes of the first through third TFTsare connected to the same gate bus line, and drain electrodes of theTFTs are connected to the same drain bus line. The first through thirdTFTs are all in an off-state in which high resistance is maintainedduring the polymer forming step.

When the high resistance state of the TFT is insufficient, a leakagecurrent can be prevented by, for example, applying a low voltage to thegate bus line or using a plurality of TFTs in a case wherein p-Si isused. Further, a leakage current can be prevented by increasing thefrequency of the AC voltage applied during polymerization.

Liquid crystal displays and methods of manufacturing the same in thepresent mode for carrying out the invention will now be described withreference to specific embodiments.

Embodiment 4-1

First, a liquid crystal display according to Embodiment 4-1 in thepresent mode for carrying out the invention will be described withreference to FIGS. 42 to 46. FIG. 42 shows a configuration of the liquidcrystal display of the present embodiment. FIG. 43 shows an equivalentcircuit of one pixel of the liquid crystal display of the presentembodiment. As shown in FIGS. 42 and 43, two pixel electrodes 116 a and116 b are formed at one pixel such that they are separated from eachother with a gate bus line 112 interposed between them. The area wherethe pixel electrode 116 a is formed constitutes a divisional area α, andthe area where the pixel electrode 116 b is formed constitutes adivisional area β. The pixel electrode 116 a is electrically connectedto a source electrode of a TFT 120 a, and the pixel electrode 116 b iselectrically connected to a source electrode of a TFT 120 b. Gateelectrodes of the TFTs 120 a and 120 b are electrically connected to thesame gate bus line 112, and drain electrodes of the TFTs areelectrically connected to the same drain bus line 114.

A common electrode 142 (not shown in FIG. 42) constitutes one electrodeof each of liquid crystal capacitances Clc1 and Clc2. The pixelelectrode 116 a constitutes another electrode of the liquid crystalcapacitance Clc1 and constitutes one electrode of a storage capacitorCs1. The pixel electrode 116 b constitutes another electrode of theliquid crystal capacitance Clc2 and constitutes one electrode of astorage capacitor Cs2. A storage capacitor bus line 118 constitutesanother electrode of each of the storage capacitors Cs1 and Cs2. Thepair of the liquid crystal capacitance Clc1 and the storage capacitorCs1 and the pair of the liquid crystal capacitance Clc2 and the storagecapacitor Cs2 are parallel-connected to each other.

What is required to achieve different pre-tilt angles of liquid crystalmolecules in the two areas α and β is to fabricate the liquid crystaldisplay panel such that each of the divisional areas has a differentcapacitance ratio between the liquid crystal capacitance Clc and thestorage capacitor Cs, thereby allowing different voltages to be appliedto the liquid crystal 106. That is, the liquid crystal display panel isto be fabricated to satisfy the following expression.Cs1/(Cs1+Clc1)≠Cs2/(Cs2+Clc2)

For example, in order to apply voltages to the liquid crystal 106 in thedivisional areas α and β such that there will be a difference of 10 V,the AC voltage is set at ±30 V, and ratios Clc1:Cs1 and Clc2:Cs2 are setat 200 fF:150 fF (1 fF=10⁻¹⁵ F) and 50 fF:164 fF, respectively. Thus, avoltage of ±13 V is applied to the liquid crystal 106 in the divisionalarea α, and a voltage of ±23 V higher than that in the divisional area αis applied to the liquid crystal 106 in the divisional area β.Therefore, the pre-tilt angle in the divisional area β becomes smallerthan the pre-tilt angle in the divisional area α.

In order to make the capacitances formed in the divisional areas α and β(the sums of Clc and Cs) equal to each other, for example, the ACvoltage is set at ±23 V, and ratios Clc1:Cs1 and Clc2:Cs2 are set at 200fF:150 fF and 50 fF:300 fF, respectively. Thus, a voltage of ±10 V isapplied to the liquid crystal 106 in the divisional area α, and avoltage of ±20 V is applied to the liquid crystal 106 in the divisionalarea β. Therefore, the pre-tilt angle in the divisional area β becomessmaller than the pre-tilt angle in the divisional area α.

FIG. 44 shows a modification of the configuration of the liquid crystaldisplay of the present embodiment. In the present modification, as shownin FIG. 44, a TFT 120 b is formed between a drain bus line 114 and apixel electrode 116 b, and a TFT 120 a is formed between the pixelelectrode 116 b and a pixel electrode 116 a. That is, a drain electrodeof the TFT 120 b is connected to the drain bus line 114, and a sourceelectrode of the TFT is connected to the pixel electrode 116 b. A drainelectrode of the TFT 120 a is connected to the pixel electrode 116 b,and a source electrode of the TFT is connected to the pixel electrode116 a. Gate electrodes of the TFTs 120 a and 120 b are parts of the samegate bus line 112. The pixel electrodes 116 a and 116 b are separatedfrom each other with the TFT 120 a interposed between them. For example,when TFTs formed using p-Si are used, three or more divisional areas maybe formed, and TFTs connected to respective divisional areas may beconnected in series.

FIG. 45 shows another modification of the configuration of the liquidcrystal display of the present embodiment. In the present modification,as shown in FIG. 45, a TFT 120 a is formed between a drain bus line 114and a pixel electrode 116 a, and a TFT 120 b is formed between the pixelelectrode 116 a and a pixel electrode 116 b. That is, a drain electrodeof the TFT 120 a is connected to the drain bus line 114, and a sourceelectrode of the TFT is connected to the pixel electrode 116 a. A drainelectrode of the TFT 120 b is connected to the pixel electrode 116 a,and a source electrode of the TFT is connected to the pixel electrode116 b. Gate electrodes of the TFTs 120 a and 120 b are parts of the samegate bus line 112. The pixel electrodes 116 a and 116 b are separatedfrom each other with the TFT 120 b interposed between them.

FIG. 46 shows still another modification of the configuration of theliquid crystal display of the present embodiment. In the presentmodification, as shown in FIG. 46, a TFT 120 b is formed between a pixelelectrode 116 a and a pixel electrode 116 b. A gate electrode of a TFT120 a is part of a gate bus line 112, and a gate electrode of the TFT120 b is part of another gate bus line 112′. A storage capacitor Cs1 isformed between the pixel electrode 116 a and a storage capacitor busline 118, and a storage capacitor Cs2 is formed between a storagecapacitor electrode 119 electrically connected to the pixel electrode116 a and the storage capacitor bus line 118. The pixel electrodes 116 aand 116 b are separated from each other with the TFT 120 b interposedbetween them. The TFT 120 b is in the off-state at the step ofirradiating the liquid crystal 106 with UV light. A predeterminedvoltage is always applied to the gate bus line 112′ during actualdriving, and the TFT 120 b is always in an on-state during actualdriving.

In the present embodiment, since a different pre-tilt angle can beachieved in each of a plurality of divisional areas, it is possible toavoid the problem that a displayed image appears whitish when viewed ina direction oblique to the display screen, which allows preferabledisplay characteristics to be achieved.

Embodiment 4-2

A liquid crystal display according to Embodiment 4-2 in the present modefor carrying out the invention will now be described with reference toFIG. 47. When a liquid crystal display is actually driven, a final pixelpotential at each pixel electrode is under influence of a voltagewaveform on each bus line. In particular, a pixel potential frequentlyundergoes a significant fluctuation under the influence of a gatewaveform. In the present embodiment, the influence of fluctuations of apixel potential is suppressed by properly setting the values ofparasitic capacitances Cgs between two divisional areas α and β, forexample.

FIG. 47 shows an equivalent circuit of one pixel of a liquid crystaldisplay according to the present embodiment. As shown in FIG. 47, adivisional area a having a pixel electrode 116 a formed therein and adivisional area β having a pixel electrode 116 b formed therein areformed in the single pixel. A common electrode 142 and a storagecapacitor bus line 118 are connected after a monomer or oligomer in aliquid crystal 106 is polymerized. In general, a feed-through voltageattributable to a gate waveform during actual driving has differentvalues at the pixel electrodes 116 a and 116 b. In order to make thevalues of the feed-through voltage at the pixel electrodes 116 a and 116b substantially equal to each other, what is required is to design themagnitudes of parasitic capacitances Cgs1 and Cgs2 such that thefollowing expression is true.Cgs1/(Cs1+Clc1)=Cgs2/(Cs2+Clc2)

According to the present embodiment, any reduction in the displayquality of the liquid crystal display can be prevented. Even when thefeed-through voltage values at the pixel electrodes 116 a and 116 b arenot equal to each other, any reduction in display quality can besuppressed by designing the magnitudes of the parasitic capacities Cgs1and Cgs2 such that the following expression is true.0.7<[Cgs1/(Cs1+Clc1)]/[Cgs2/(Cs2+Clc2)]<1.3

Embodiment 4-3

A liquid crystal display according to Embodiment 4-3 in the present modefor carrying out the invention will now be described with reference toFIG. 48. FIG. 48 shows an equivalent circuit of one pixel of the liquidcrystal display of the present embodiment. As shown in FIG. 48, in thepresent embodiment, storage capacitor bus lines 118 and 118′ are formedfor divisional areas α and β, respectively. A TFT 120 which is formed ateach pixel must be designed in consideration of balance between (1) avoltage applied to a liquid crystal 106 during polymerization, (2) thecapability of driving the pixel during actual driving and (3) the ratioof the same to a pixel capacitance that compensates for variousirregularities. When the storage capacitor bus lines 118 and 118′ areindependently formed for each of the divisional areas α and β, ACvoltages having different amplitudes and frequencies can be applied tothe liquid crystal 106 in each of the divisional areas α and β using aplurality of AC power sources 174 and 174′, which will significantlyrelax the restriction pointed out in the above item (1).

Embodiment 4-4

A liquid crystal display according to Embodiment 4-4 in the present modefor carrying out the invention will be described with reference to FIG.49. FIG. 49 shows an equivalent circuit of one pixel of the liquidcrystal display of the present embodiment. As shown in FIG. 49, theliquid crystal display of the present embodiment has a Cs-on-Gatestructure in which a gate bus line 112 constitutes one electrode of astorage capacitor Cs. Storage capacitances Cs1 to Cs3 are formed betweenrespective pixel electrodes 116 a to 116 c and the gate bus line 112.The present embodiment is similar to Embodiment 4-1 in that a differentvoltage can be applied to a liquid crystal 106 in each divisional areaby fabricating the liquid crystal panel such that each divisional areahas a different capacitance ratio between a liquid crystal capacitanceClc and a storage capacitor Cs. It is also possible to combine storagecapacitors Cs formed between the pixel electrodes 116 a to 116 c and thegate bus line 12 and storage capacitors Cs formed between the pixelelectrodes 116 a to 116 c and a storage capacitor bus line 118.

The present mode for carrying out the invention makes it possible toprovide a liquid crystal display which can achieve high displaycharacteristics.

Fifth Mode for Carrying Out the Invention

A method of manufacturing a liquid crystal display in a fifth mode forcarrying out the invention will now be described with reference to FIGS.50 to 55D. The present mode for carrying out the invention relates to amethod of manufacturing a VA mode liquid crystal display in which thealignment of the liquid crystal is regulated.

MVA-LCDs have been proposed as liquid crystal displays having a wideviewing angle (see Patent Document 3, for example). In an MVA-LCD,liquid crystal molecules are aligned substantially perpendicularly to asubstrate surface when no voltage is applied. When a voltage is applied,liquid crystal molecules are divided into four areas in one pixel andare tilted in four different directions, respectively. Viewing anglecharacteristics in those areas are mixed, and a wide viewing angle isconsequently achieved.

On the contrary, Methods for providing liquid crystal molecules with apre-tilt angle include a method in which a liquid crystal display panelis filled with a liquid crystal composition including a polymerizableresin (a resin which is polymerized into a polymer liquid crystal) andin which the resin is polymerized by irradiating it with light whileapplying a voltage to the liquid crystal to obtain a pre-tilt anglehaving an azimuth in the direction in which liquid crystal molecules areinclined (see Japanese patent application No. 2002-90523 made by thepresent applicant, for example). A pre-tilt angle obtained using thismethod varies depending on the voltage applied to the liquid crystal atthe time of irradiation with light. Specifically, the pre-tilt angle ofliquid crystal molecules tends to become smaller (or the angle ofinclination from a direction perpendicular to the substrate surfaceincreases), the higher the applied voltage.

In an MVA-LCD, when white or black is displayed, a contrast ratio of 10or more is achieved at upward, downward, leftward and rightward viewingangles at an inclination of 80°. In an MVA-LCD, it is required todetermine the direction of alignment of liquid crystal molecules inadvance by forming bank-shaped alignment regulating structuresconstituted by a resin on at least either substrate.

However, a common MVA-LCD has a problem in that it has low chromaticreproducibility relative to viewing angles. The problem is encounteredwhen liquid crystal molecules are aligned in a plurality of directions.When azimuths of alignment of liquid crystal molecules are opposite toeach other (or 180° different from each other), there is a differencebetween T-V characteristics at the respective azimuths when viewed in anoblique direction. When the LCD is actually viewed in an obliquedirection, it will have T-V characteristics which are a combination ofthe T-V characteristics at the respective azimuths. Although no problemtherefore occurs in display of black and white, when a color image isdisplayed, there will be significant differences in color tones betweena view in a direction square to the display and a view in an obliquedirection.

It is therefore required to reduce changes in T-V characteristics thatoccur when the display screen is viewed in an oblique direction.Especially, inversion of T-V characteristics that occurs at lowgradations must be eliminated and, if not eliminated, differences inluminance at low gradations must be reduced.

As a method for solving this, studies are being made on a technique forimproving gradation/viewing angle characteristics in which a pluralityof T-V characteristics are combined in one pixel to moderate waviness ofa T-V curve when viewed in an oblique direction. There are variouspossible methods for varying T-V characteristics in one pixel. Let usnow consider realizing a state in which liquid crystal molecules have aplurality of pre-tilt angles in one pixel.

In the present mode for carrying out the invention, the following methodis used to vary a pre-tilt angle in one pixel utilizing the phenomenonthat a pre-tilt angle of a liquid crystal mixed with a polymericcomponent changes as a result of a change of a voltage applied to theliquid crystal when irradiating it with light.

(1) When a liquid crystal is irradiated with light, only part of onepixel is allowed to be irradiated using a mask instead of uniformlyirradiating the pixel as a whole.

(2) When the area irradiated with light is moved, the applied voltage ischanged.

A plurality of pre-tilt angles can be provided in one pixel using theabove-described method. A plurality of T-V characteristics can be thusprovided in one pixel, and differences in viewing angle characteristicsbetween a view in an oblique direction and a view in a square directioncan be reduced when the characteristics are combined. This contributesto a reduction of drifts of chromaticity in the view in an obliquedirection. The present mode for carrying out the invention will now bedescribed with reference to specific embodiments.

Embodiment 5-1

First, a method of manufacturing a liquid crystal display according toEmbodiment 5-1 in the present mode for carrying out the invention willbe descried with reference to FIGS. 50 to 52D. FIG. 50 shows aconfiguration of one pixel of a liquid crystal display fabricated usingthe method of manufacturing a liquid crystal display according to thepresent embodiment. FIG. 51 shows a schematic sectional configuration ofthe liquid crystal display taken along the line A-A in FIG. 50. As shownin FIGS. 50 and 51, one pixel of the liquid crystal display has twoalignment regions in which liquid crystal molecules 107 are tilted indifferent directions.

Drain bus lines 114 and gate bus lines 112 both having a width of 7 μmare formed on a TFT substrate 102. Pixel electrodes 116 which are solidelectrodes constituted by ITOs are formed at pixel regions defined bythe bus lines 112 and 114. For example, the pitch of the pixels in thelongitudinal direction thereof (or the direction in which the drain buslines 114 extend, which holds true hereinafter) is 300 μm. On thecontrary, for example, the pitch of the pixels in the transversedirection thereof (or the direction in which the gate bus lines 112extend, which holds true hereinafter) is 100 μm. Storage capacitorelectrodes 119 are provided substantially in the middle of the pixelregions.

A pixel electrode 116 may be formed with, for example, fine slitsextending in a plurality of directions in order to control the alignmentof a liquid crystal 106. A pixel electrode 116 may be formed bycombining a plurality of electrode units which are in one or pluraltypes of configurations and which are adjacent to each other with slitsinterposed between them.

Although not shown, a black matrix (BM) having a width of 23 μm in thelongitudinal direction thereof are provided on an opposite substrate 104provided opposite to the TFT substrate 102, the black matrix havingpitches of 300 μm and 100 μm which are the same the pixel pitches. CFresin layers in red, green and blue are formed at each opening of theblack matrix. A common electrode 142 which is a solid electrodeconstituted by an ITO is formed throughout the substrate over the CFresin layers. A liquid crystal (a liquid crystal composition) 106including a polymerizable resin (which is polymerized into a polymerliquid crystal) is charged and sealed between the substrates 102 and104.

The liquid crystal display panel having the above-describedconfiguration is irradiated with light from the side of the oppositesubstrate 104 to polymerize the polymeric component. A pixel ispartially irradiated with light using a mask (photo-mask) 150 instead ofirradiating the pixel as a whole with light. Specifically, the mask 150used here has openings 151 in the form of slits having a width of, forexample, 20 μm and extending in the horizontal direction in the figure.The width of the opening 151 is smaller than the width of the pixelregion in the vertical direction in the figure. The openings 151 areprovided at a pitch of 300 μm which is the same as the pixel pitch.

FIGS. 52A to 52D are sectional views showing the method of manufacturingthe liquid crystal display according to the present embodiment. First,as shown in FIG. 52A, the mask 150 is placed directly above the oppositesubstrate 104 with a central section of a pixel region aligned with anopening 151. When scattered light 152 is projected from above the mask150, the liquid crystal 106 in an area a is irradiated with the light152 through the opening 151 to polymerize the polymeric component. Atthis time, a voltage of 0 V is applied (no voltage is applied) to theliquid crystal 106. In the area a, the pre-tilt angle becomes thevertical (90°) because the polymeric component is polymerized with novoltage applied.

Next, as shown in FIG. 52B, the mask 150 is elevated relative to theliquid crystal display panel (to provide an interval of 50 μm betweenthe bottom surface of the mask 150 and the top surface of the oppositesubstrate 104, for example) without making any change in the positionalrelationship between the central section of the pixel region and theopening 151 in a plan view. Since the interval between the mask 150 andthe liquid crystal panel increases, the area irradiated with the light152 through the opening 151 is increased, and an area b will now beirradiated with the light 152 in addition to the area a. At this time,for example, a voltage of 2.5 V is applied to the liquid crystal 106. Asa result, the area b is irradiated with the light 152 in a state inwhich liquid crystal molecules 107 are inclined. Since the area b isthus irradiated with light while the liquid crystal is inclined, apredetermined pre-tilt angle is achieved in the direction in which theliquid crystal molecules are inclined. No change occurs in the pre-tiltangle which has already been achieved in the area a.

Thereafter, as shown in FIGS. 52C and 52D, the range irradiated with thelight 152 is gradually extended, and the voltage applied to the liquidcrystal 106 is gradually increased. As a result, liquid crystalmolecules 107 in the area a in the middle of the pixel are provided witha great pre-tilt angle, and liquid crystal molecules in areas b, c and dare provided with respective pre-tilt angles that become smaller in theorder in which the areas are listed above. That is, since liquid crystalmolecules 107 in one pixel can be provided with a plurality of pre-tiltangles, the single pixel has a plurality of T-V characteristics. Thismakes it possible to improve chromatic characteristics when viewed in anoblique direction.

Embodiment 5-2

A method of manufacturing a liquid crystal display according toEmbodiment 5-2 in the present mode for carrying out the invention willnow be described with reference to FIGS. 53A to 53D. FIGS. 53A to 53Dare sectional views showing the method of manufacturing a liquid crystaldisplay according to the present embodiment. The present embodiment ischaracterized in that a mask 150 is moved in a direction different fromthat in Embodiment 5-1. As shown in FIGS. 53A to 53D, in the presentembodiment, the mask 150 is moved from a central section of a pixelregion in the longitudinal direction of the same (the horizontaldirection in FIGS. 53 a to 53D) to move the range of irradiation withlight 152 gradually, and a voltage applied to a liquid crystal 106 isgradually increased. As a result, liquid crystal molecules 107 in anarea a in the middle of the pixel is provided with a great pre-tiltangle, and liquid crystal molecules 107 in areas b, c and d are providedwith respective pre-tilt angles which gradually decrease in the order inwhich the areas are listed above. That is, since liquid crystalmolecules 107 in one pixel can be provided with a plurality of pre-tiltangles, the single pixel has a plurality of T-V characteristics. Thismakes it possible to improve chromatic characteristics when viewed in anoblique direction.

Embodiment 5-3

A method of manufacturing a liquid crystal display according toEmbodiment 5-3 in the present mode for carrying out the invention willnow be described with reference to FIGS. 54A to 54D. FIGS. 54A to 54Dare sectional views showing the method of manufacturing a liquid crystaldisplay according to the present embodiment. In comparison to Embodiment5-1, the present embodiment is characterized in that an optical systemcapable of controlling scattering of light to change scattering of light152 without moving a mask 150. As shown in FIG. 54A, an opening 151 inthe mask 150 is smaller in width than a pixel region and positionedabove a central section of the pixel. At an initial phase, since thescattering of the light 152 is relatively small, the area irradiatedwith the light 152 is small. Thereafter, the scattering of the light isgradually increased as shown in FIGS. 54B to 54D, and a voltage appliedto a liquid crystal 106 is gradually increased. As a result, liquidcrystal molecules 107 in an area a in the middle of the pixel isprovided with a great pre-tilt angle, and liquid crystal molecules 107in areas b, c and d are provided with respective pre-tilt angles whichgradually decrease in the order in which the areas are listed above.That is, since liquid crystal molecules 107 in one pixel can be providedwith a plurality of pre-tilt angles, the single pixel has a plurality ofT-V characteristics. This makes it possible to improve chromaticcharacteristics when viewed in an oblique direction.

Embodiment 5-4

A method of manufacturing a liquid crystal display according toEmbodiment 5-4 in the present mode for carrying out the invention willnow be described with reference to FIGS. 55A to 55D. FIGS. 55A to 55Dare sectional views showing the method of manufacturing a liquid crystaldisplay according to the present embodiment. The present embodimentincludes a step of forming a mask 154 constituted by, for example, ametal layer on a surface of a glass substrate 111 constituting anopposite substrate 104 which is to be irradiated by light (the topsurface in FIGS. 55A to 55D) before radiating light 152. The presentembodiment also includes a step of removing the mask 154 after apolymeric component in a liquid crystal 106 is polymerized byirradiating it with the light 152. The present embodiment also employsan optical system capable of controlling scattering of light similarlyto Embodiment 5-3 to change scattering of the light 152.

As shown in FIG. 55A, the mask 154 is formed with an opening 151 havinga smaller width than the width of a pixel region, located above acentral section of the pixel region. At an initial phase, since thescattering of the light 152 is relatively small, the area irradiatedwith the light 152 is small. Thereafter, the scattering of the light isgradually increased as shown in FIGS. 55B to 55D, and a voltage appliedto the liquid crystal 106 is gradually increased. As a result, liquidcrystal molecules 107 in an area a in the middle of the pixel isprovided with a great pre-tilt angle, and liquid crystal molecules 107in areas b, c and d are provided with respective pre-tilt angles whichbecome smaller in the order in which the areas are listed above.Thereafter, the mask 154 formed on the glass substrate 111 is removed.In the present embodiment, since liquid crystal molecules 107 in onepixel can be provided with a plurality of pre-tilt angles, the singlepixel has a plurality of T-V characteristics. This makes it possible toimprove chromatic characteristics when viewed in an oblique direction.

The invention is not limited to the above-described modes for carryingout the same and may be modified in various ways.

For example, although transmissive liquid crystal displays have beenreferred to as examples in the above-described mode for carrying out theinvention, the invention is not limited to them and may be applied toother types of liquid crystal displays such as reflective types andtransflective types.

Although liquid crystal displays having color filters on an oppositesubstrate 104 have been referred to as examples in the above-describedmodes for carrying out the invention, the invention is not limited tothem and may be applied to liquid crystal displays having the so-calledCF-on-TFT structure in which color filters are formed on a TFT substrate102.

Sixth Mode for Carrying Out the Invention

The present mode for carrying out the invention relates to a liquidcrystal display and, particularly, to a multi-domain vertical alignment(MVA) type liquid crystal display in which the direction of alignment ofa liquid crystal at the time of application of a voltage is controlledsuch that it becomes a plurality of directions utilizing structuresformed on the substrates. In the field of MVA type liquid crystaldisplays, it is desired to improve the stability of liquid crystalalignment without sacrificing ease of manufacture and displayperformance and to make improvements with respect to responsecharacteristics and display defects.

Recently, liquid crystal displays have been put in a wide variety ofapplications by taking advantage of their features such as low profiles,light weights, drivability at low voltages and low power consumption.

However, liquid crystal panels are presently inferior to CRTs in displaycharacteristics when viewed in an oblique direction or viewing anglecharacteristics. Therefore, there is a demand for liquid crystal panelshaving high viewing angle characteristics. A liquid crystal display haslow viewing angle characteristics because an angle that a light beamincident upon the panel makes with liquid crystal molecules variesdepending on the direction of incidence. Multi-domain vertical alignment(MVA) liquid crystal panels have been put in use as liquid crystalpanels having high viewing angle characteristics, and a configuration ofthe same is disclosed in Japanese Patent Laid-Open No. JP-A-11-242225.

FIG. 56 shows an example of a sectional shape of a vertical alignment(VA) type liquid crystal display. The liquid crystal display is obtainedby combining two glass substrates 202 and 205 with spacers 207 disposedbetween them to provide a predetermined thickness, sealing thesubstrates at the peripheries thereof with a seal material 203, andthereafter injecting a liquid crystal to form and enclose a liquidcrystal layer 204 therein. Polarizers 201 and 206 are provided on bothsides of the combined substrates 202 and 205. Further, a phasedifference film may be provided. An electrode pattern for driving isformed on a surface of at least either of the two glass substrates 202and 205 (the substrate 205 in this case), and drive signals are appliedfrom the outside through terminals provided at the section indicated byreference number 208. Vertical alignment films are formed on electrodeson the glass substrates in an MVA type display.

FIG. 57 shows an example of an electrode pattern of an MVA type liquidcrystal display. In TFT type liquid crystal displays that are presentlythe mainstream from the technical point of view, a plurality of gate buslines 211 are provided in parallel with each other; a plurality of drainbus lines 212 are provided in parallel with each other in a directionperpendicular to the drain bus lines 211; pixel electrodes 215 areprovided in regions partitioned by the gate bus lines 211 and the drainbus lines 212; and TFTs 213 for driving the pixel electrodes 215 areprovided at intersections between the gate bus lines 211 and the drainbus lines 212. Further, Cs bus lines 214 are provided between the gatebus lines 211, and auxiliary capacitor electrodes 218 are provided inparts of the pixel electrodes 215 that overlap the bus lines 214.

FIGS. 58A and 58B illustrate alignment control exercised by structures(protrusions (banks) on electrodes in this case) of an MVA type liquidcrystal display. FIG. 58A shows a state in which no voltage is applied,and FIG. 58B shows a state in which a voltage is applied. As shown inFIG. 58A, a transparent opposite electrode 220 which spreads throughouta display surface is formed on a glass substrate 202. Protrusions 231are formed on the electrodes, and a vertical alignment film 222 isformed on the same. Pixel electrodes 215 are formed on a glass substrate205. Protrusions 231 are formed on the electrodes, and a verticalalignment film 222 is further formed on the same.

As shown in FIG. 58A, in the no voltage applied state, i.e., when novoltage is applied between the pixel electrodes 215 and the oppositeelectrode 220, liquid crystal molecules 210 are aligned substantiallyperpendicularly to the substrates 202 and 205. However, the liquidcrystal molecules are aligned at a slight inclination in the vicinity ofthe protrusions 231 under the influence of inclined surfaces of theprotrusions. As shown in FIG. 58B, when a voltage is applied between thepixel electrodes 215 and the opposite electrode 220, the liquid crystalmolecules 210 are tilted by an electric field. Although the tiltingdirection (alignment direction) is not regulated by simply applying thevoltage, the liquid crystal molecules 210 in the vicinity of theprotrusions 231 are tilted toward a direction perpendicular to thesurfaces of the protrusions 231 when no voltage is applied as describedabove, and neighboring liquid crystal molecules are therefore alignedaccording to those pre-tilted liquid crystal molecules. That is, thereare different alignment directions originating in the protrusions 231that serve as boundaries. Since the an alignment direction originatingin a protrusion on the glass substrate 202 is the same as an alignmentdirection originating in a protrusion on the glass substrate 205adjacent to the protrusion on the substrate 202, a stable state ofalignment is established between the protrusions on the two glasssubstrates adjacent to each other. Such a technique for forming areashaving different directions of alignment of a liquid crystal is referredto as “domain division technique”, and an area in which liquid crystalmolecules are aligned in the same direction is referred to as “domain”.

While FIGS. 58A and 58B show an example in which protrusions that aredielectric bodies provided on electrodes are used as structures foralignment controlling, it is possible to use electrode slits provided byremoving parts of electrodes in a display area or recesses on dielectriclayers provided on the electrodes as structures for alignment control onthe electrodes.

FIG. 59 shows an example in which electrode slits 216 provided on apixel electrode 215 are used as structures for alignment control. Asillustrated, the electrode slits 216 and an a region 217 between pixelelectrodes 215 adjacent to each other serve as structures for alignmentcontrol to divide the alignment direction of liquid crystal molecules.

In the electrode pattern in FIG. 57, the pixel electrode slits 216 andthe protrusions 217 provided on the opposite substrate are alternatelydisposed in parallel with each other, and the extending directions ofthe pixel electrode slits 216 and the protrusions 217 in the upper andlower halves of the pixel are 90° different from each other. As aresult, the single pixel region is divided into areas in which theliquid crystal is inclined in respective four directions, i.e., fourdomains. When four domains are formed in one pixel region as thusdescribed, viewing angle biases can be averaged compared to those in acase where the liquid crystal is inclined only in one direction, whichallows a significant improvement of viewing angle characteristics.

Domain dividing structures may be provided on both substrates or oneither substrate. Although the protrusions in FIGS. 58A and 58B areformed on both of substrates by way of example, they may be providedonly on either of the substrates. Similarly, although the electrodeslits in FIG. 59 are provided on either of the substrates, they may beprovided on both of the substrates. Further, both of electrode slits andprotrusions may be provided as shown in FIG. 57.

FIG. 60 shows results of measurement of applied voltage/transmittancecharacteristics (T-V characteristics) of an MVA type liquid crystaldisplay taken from a direction square to the display and a direction atan upward angle of 60° from the same. There is a problem in that adistortion in luminance transition occurs in the portion indicated bythe circle P in the figure. For example, the point having a relativelylow luminance which is indicated by Q in the graph representing the viewin the square direction becomes brighter at the upward angle of 60°. Onthe contrary, the point having a relatively high luminance indicated byR becomes darker. As a result, the difference in luminance between thosepoints disappears in the view in the oblique direction. This phenomenonmost significantly appears as changes in colors. The color of an imagediscolors into a whitish tint when viewed in an oblique direction. Anexamination of gradation histograms of three colors, R, G and B of theimage indicates that the image becomes whitish because the distributionof red having a relatively high brightness changes darker, and green andblue which are originally dark become brighter. The phenomenon is hereinreferred to as whitish discoloration.

As an approach for mitigation of the whitish discoloration, a method isknown in which one pixel is formed by a plurality of sub-pixels and inwhich all sub-pixels are capacitively coupled in terms of electricalrelationship. When a voltage is applied through a transistor, since thepotential is divided according to the capacitance ratio between thesub-pixels, a different voltage is applied to each of the sub-pixels toprovide the sub-pixels with different T-V characteristics. As a result,as shown in FIG. 61, transmittance at bright pixels starts increasing atrelatively low applied voltages, and transmittance at darker pixelsstarts increasing at higher applied voltages. By setting the ratiobetween the brighter pixels and darker pixels appropriately, thebrighter pixels will have transmittance characteristics indicated by A;the darker pixels will have transmittance characteristics indicated byB; and composite transmittance characteristics C will be provided by thepixels as a whole. Since a characteristics distortion is thusdistributed among the plurality of sub-pixels, the distortion becomesless perceptible. Such a method is referred to as “HT(halftone/grayscale) method utilizing capacitive coupling”.

However, the HT method utilizing capacitive coupling has a problem inthat it involves a very complicated structure which is liable to causedefects and difficult to manufacture and in that it results in asignificant reduction of an aperture ratio.

The HT method utilizing capacitive coupling is also problematic in thatit involves a high driving voltage. This is because a voltage loss iscaused by capacitive coupling, and the driving voltage increases withthe number of divisions. An increase in the driving voltage necessitatesa driver IC having a higher withstand voltage, which is disadvantageousin terms of cost.

Further, according to the HT method utilizing capacitive coupling,characteristics are digitally synthesized because a potential differenceis provided from sub-pixel to sub-pixel. This results in a problem thatthe method provides characteristics lower than an ideal state in which achange occurs in a linear manner with a slope.

Since the HT method utilizing capacitive coupling has so significantproblems as thus described although it is effective, no product iscurrently being manufactured by employing the method.

It is an object of the present mode for carrying out the invention toimplement the HT method using a simpler configuration in an MVA typeliquid crystal display.

In the present mode for carrying out the invention, attention is paid tothe fact that a threshold voltage of an MVA type liquid crystal displayvaries depending on the density of structures used therein, and the HTmethod is implemented by varying the threshold voltage in one pixelregion by varying the density of structures in the pixel. In an MVA typeliquid crystal display, structures as alignment control units are used,and the density of the structures can be varied by changing the patternof the structures. It is therefore possible to vary the density of thestructures easily without, for example, increasing manufacturing steps,and the HT method can be thus implemented by varying the thresholdvoltage locally.

FIGS. 62A and 62B illustrate disposing densities of protrusions used asalignment controlling structures. FIG. 62A shows a case in whichprotrusions 231 each extending in one direction are alternately providedon electrodes 241 and 242 on two substrates 202 and 205. Although notshown, vertical alignment films are formed on the electrodes andprotrusions. The width of the protrusions 231 is represented by L, andan interval between adjoining protrusions 231 is represented by S. FIG.62B shows a case in which protrusions 231 extending in one direction areprovided only on an electrode on one of substrates. In this case again,a vertical alignment film is formed on the electrode and theprotrusions. The width of the protrusions 231 is represented by L, andan interval between adjoining protrusions 231 is represented by S.

FIG. 63 shows T-V characteristics of an MVA type liquid crystal displayhaving protrusions as shown in FIG. 62A as alignment controllingstructures, obtained while varying the interval S between adjoiningprotrusions. In this apparatus, the thickness (cell thickness) of theliquid crystal layer was 4 μm; the height of the protrusions (banks) was1.5 μm; the width L of the protrusions was 5 μm a negative liquidcrystal manufactured by Merck was used as the liquid crystal; andvertical alignment films manufactured by JSR Corporation were used asalignment films.

FIG. 64 shows changes in a threshold voltage relative to the interval Sbetween the adjoining protrusions. FIGS. 63 and 64 indicate that whenthe interval S between the adjoining protrusions is decreased below 10μm, the threshold voltage is decreased by 0.5 V to 1V from values atintervals S in the range from 15 to 25 μm. That is, the thresholdvoltage decreases when the interval S between the adjoining protrusionsis about three times the cell thickness or less.

FIGS. 65A and 65B illustrate the reason of this. As shown in FIG. 65A,when the interval S is small, liquid crystal molecules 210 between theadjoining protrusions 231 are tilted (pre-tilted) even when no voltageis applied. Thus, the liquid crystal molecules 210 can be tilted at alower voltage. As shown in FIG. 65B, when the interval S is greater thanthe above-described condition, the liquid crystal molecules 210 betweenthe adjoining protrusions 231 are less susceptible to the influence ofthe protrusions and are aligned substantially perpendicularly to thesubstrate surfaces when no voltage is applied. The vertically alignedarea is unlikely to be tilted because the longitudinal direction of theliquid crystal molecules is in parallel with the direction of anelectric field, and no reduction of the threshold therefore occurs. Thisresults in an operation similar to that in an ordinary MVA type liquidcrystal display in which tilting is triggered by a pre-tilt of theliquid crystal in the vicinity of protrusions.

FIG. 66 shows T-V characteristics of an MVA type liquid crystal displayhaving protrusions as shown in FIG. 62B as alignment controllingstructures, obtained while varying the interval S between adjoiningprotrusions. The condition of this apparatus was otherwise similar tothat in FIG. 63. The thickness (cell thickness) of the liquid crystallayer was 4 μm; the height of the protrusions (banks) was 1.5 μm; thewidth L of the protrusions was 5 μm; MJ961213 was used as the liquidcrystal; and JALS-684 was used as the alignment film.

FIG. 66 indicates that when the protrusions (banks) are provided only onone of the substrates, a reduction in the interval S between theprotrusions results in a threshold voltage 0.8 V higher than thethreshold voltage of an MVA according to the related art in which upperand lower protrusions are provided at a greater interval.

FIGS. 67A to 67C illustrate behaviors of a liquid crystal in a casewherein protrusions (banks) are provided only on one substrate in a highdensity. In this case, liquid crystal molecules behave according to aprinciple completely different from that of the behaviors of liquidcrystal molecules described with reference to FIGS. 65A and 65B. Asshown in FIG. 67A, liquid crystal molecules 210 are very slightly tiltedat an orientation perpendicular to protrusions (banks) 231 when a smallvoltage is applied. This is considered attributable to the fact thatthey cannot be sufficiently tilted because the adjacent protrusions 231are located very close to each other although the orientations of theirtilts relative to the adjacent protrusions are 180° different.Therefore, substantially no light is transmitted. When the appliedvoltage is increased in this state, although the liquid crystalmolecules 210 are tilted further, they cannot be tilted in thedirections of the 180° different alignment orientations because theadjacent protrusions 231 are located very close. As a result, as shownin FIG. 67B, the orientations of the tilts of the liquid crystalgradually change from the directions at 90° to the direction in whichthe protrusions extend, and the alignment orientations become inclinedrelative to the extending direction of the protrusions. The liquidcrystal molecules cannot be sufficiently tilted still in this state.When the applied voltage is further increased, the alignmentorientations become parallel to the extending direction of theprotrusions as shown in FIG. 67C. The liquid crystal molecules can besufficiently tilted in this state. It is considered that the liquidcrystal molecules are difficult to tilt with a low applied voltagebecause their alignment is oppositely oriented by the adjacentprotrusions as thus described and that the threshold voltage isconsequently increased.

As described above, a threshold voltage can be reduced by about 0.5 V to1V by providing protrusions on both substrates as shown in FIG. 62A andby setting the interval S between the protrusions equal to or smallerthan about three times the cell thickness, and the threshold voltage canbe increased by about 0.8 V by providing protrusions only on onesubstrate as shown in FIG. 62B and setting the interval S between theprotrusions smaller. Therefore, viewing angle characteristics can beimproved using the HT method by disposing protrusions as shown in FIGS.62A and 62B to provide a first area having a high threshold voltage anda second area having a low threshold voltage in one pixel region.

The first area and the second area may be provided on either or both offirst and second substrates. When only either of the first and secondsubstrates has the first area and the second area, no structure to beused as an alignment controlling unit is provided on the other substrateor, if provided, linear structures are provided in a face-to-facerelationship with the second area on the substrate.

When the first area and the second area are provided on both of thefirst and second substrates, they are disposed such that the first areaon the first substrate faces the second area on the second substrate andthe first area on the second substrate faces the second area on thefirst substrate.

A plurality of linear structures provided in the first area and aplurality of linear structures provided in the second area may besubstantially in parallel with each other, and they may alternativelyextend in directions orthogonal to each other.

The structures may be provided as protrusions protruding into the liquidcrystal layer, recesses which are sunk oppositely to the liquid crystallayer or electrode slits which are local blanks in electrodes in adisplay area. It is desirable for any of the structures that at leastany of the width, the pitch of arrangement and the electrical resistanceof the structures is varied between the first and second areas toachieve desired threshold voltage characteristics.

Embodiment 6-1

An MVA type liquid crystal display of the present embodiment is similarin configuration to MVA type liquid crystal displays according to therelated art except for the pattern of protrusions (banks) used asalignment regulating structures. Various exemplary patterns may beemployed for protrusions (banks) of the MVA type liquid crystal displayof the present embodiment.

FIGS. 68A to 68C show sections of patterns for the protrusions (banks)of the MVA type liquid crystal display of the present embodiment. FIGS.69A and 69B show plan configurations of patterns for the protrusions(banks) of the MVA type liquid crystal display of the presentembodiment. As shown in FIGS. 68A to 69B, in the present embodiment, aplurality of protrusions (banks) 231 extend in the same direction inparallel with each other.

In the example shown in FIG. 68A, protrusions 231 are provided only onan electrode 242 on one substrate 205. As illustrated, three protrusions231 disposed close to each other at intervals S1 are grouped, andresultant groups are disposed at greater intervals S2. The protrusionshave a width of 3 μm, and the interval S1 is, for example, 3 μm, and theinterval S2 is, for example, 30 μm. A threshold voltage is high in anarea A in which the protrusions are disposed close to each other, and athreshold voltage in an area B in which intervals between adjoiningprotrusions are greater is lower than the threshold voltage in the areaA. In the area B, since alignment orientations exerted by theprotrusions on both sides are 180° different from each other, a domainboundary is formed in the middle. Since the position of the domainboundary cannot be controlled, this example has a problem in that domainsizes are unstable.

In the example shown in FIG. 68B, three protrusions 231 disposed closeto each other at intervals S1 on each of electrodes 241 and 242 on twosubstrates 202 and 205 are grouped; resultant groups are disposed atgreater intervals S3; and groups each comprising three protrusions 231provided on the upper and lower substrates adjacent to each other aredisposed such that they are at equal intervals S4. For example, theinterval S1 is 3 μm, and the interval S4 is 25 μm. A threshold voltageis high in an area D in which the protrusions are disposed close to eachother, and a threshold voltage in areas C and E in which intervalsbetween adjoining protrusions are greater is lower than the thresholdvoltage in the area D. A stable domain can be formed in one direction inthe areas C and E, and alignment orientations in the areas C and D are180° different from each other. The interval S4 is set at 10 μm or lessto make a threshold voltage difference between the areas C and Esmaller.

In the example shown in FIG. 68C, three protrusions 231 disposed closeto each other at intervals S1 on an electrode 242 on one substrate 205are grouped, and resultant groups are disposed at greater intervals S5.Individual protrusions 231 are formed at still greater intervals S6 onan electrode 241 on another substrate 202, and protrusions 231 on theupper and lower substrates adjacent to each other are disposed such thatthey are at equal intervals S7. For example, the interval S1 is 3 μm,and the interval S7 is 25 μm. A threshold voltage is high in an area Hin which the protrusions are disposed close to each other, and athreshold voltage in areas F and Gin which intervals between adjoiningprotrusions are greater is lower than the threshold voltage in the areaH. A stable domain can be formed in one direction in the areas F and G,and alignment orientations in the areas F and G are 180° different fromeach other. Also in this case, the interval S7 is set at 10 μm or lessto make a threshold voltage difference between the areas F and Gsmaller.

FIGS. 69A and 69B illustrate examples of plan configurations of patternsfor the protrusions of the present embodiment. FIG. 69A shows an examplein which protrusions (banks) extend in parallel with shorter sides of arectangular pixel electrode 215, FIG. 69A corresponding to the sectionalconfiguration shown in FIG. 68A or 68B. In a case as shown in FIG. 68A,groups of protrusions 231A and groups of protrusions 231B are bothdisposed on one substrate. In a case as shown in FIG. 68B, groups ofprotrusions 231A are disposed on one substrate, and groups ofprotrusions 231B are disposed on another substrate. When either of thegroups of protrusions 231A and the groups of protrusions 231B isreplaced with individual protrusions (banks), the example corresponds tothe example shown in FIG. 68C. A threshold voltage is high in the areaof each group in which three protrusions are provided close to eachother, and the threshold voltage is lower in an area in which adjacentprotrusions belonging to different groups are at a greater interval.

FIG. 69B shows an example similar to the example in FIG. 57, in whichprotrusions (banks) extending in directions at 45° and −45° to a side ofa rectangular pixel electrode 215 are present in a pixel region. Threeparallel protrusions (banks) 231A close to each other and one protrusion231C are provided on one substrate, and a protrusion 231B is provided onanother substrate. A threshold voltage is high in the area of the groupof the protrusions 231A in which the three protrusions are providedclose to each other, and the threshold voltage is lower in the areabetween the group of the protrusions 231A and the protrusion 231B and inthe area between the protrusions 231B and 231C. The pattern of theprotrusions shown as a plan view in FIG. 69B may be provided usingprotrusions having a sectional configuration as shown in FIG. 68A, 68Bor 68C.

Examples of sectional configurations and plan configurations of patternsof protrusions according to the present embodiment have been describedwith reference to FIGS. 68A to 69B, and various modifications may bemade to the sectional configurations and plan configurations of patternsof protrusions according to the present embodiment.

FIG. 70 shows values of T-V characteristics actually measured on adisplay having a sectional configuration as shown in FIG. 68B, a cellthickness of 4 μm, a protrusion width of 3 μm, a protrusion height of1.5 μm, protrusion intervals S1 of 3 μm and protrusion intervals S4 of25 μm. A negative liquid crystal manufactured by Merck was used as theliquid crystal; vertical alignment films manufactured by JSR Corporationwere used as the alignment films; and areas D having a high thresholdvoltage occupied 48% of the entire measured region in terms of arearatio. The result was in preferable agreement with simulation valuescalculated using the graphs shown in FIGS. 63 and 66.

Embodiment 6-2

FIG. 71 shows a section of a pattern of protrusions (banks) of an MVAtype liquid crystal display according to Embodiment 6-2. In the presentembodiment, protrusions (banks) 231A and 231B having a width L1extending in a first direction are alternately provided on substrates202 and 205 at great intervals S11+S12, and protrusions 232 having awidth S21 extending in a second direction that is perpendicular to thefirst direction are provided on both sides of protrusions 231A on thesubstrate 202 at small intervals S22. The height of the protrusions 231Aand 231B is represented by h1, and the height and length of theprotrusions 232 are represented by h2 and S11, respectively. Forexample, the cell thickness is 4 μm; L1 is 10 μm; S11 is 5 μm; S12 is 20μm; h1 is 1.5 μm; and h2 is 0.5 μm.

In the apparatus of the present embodiment, since the height of theprotrusions 232 was small, a threshold voltage in areas in aface-to-face relationship with the protrusions 232 was lower than anormal threshold voltage in areas I between the protrusions just as seenin the area between the protrusions in FIG. 62A. In this case,therefore, an operation according to the HT method took place betweenthe areas having the normal threshold voltage and the areas having thethreshold voltage lower than the same.

On the contrary, the threshold voltage in the area in a face-to-facerelationship with the protrusions 232 increased beyond the thresholdvoltage in the areas I when h2 was set equal to h1 or 1.5 μm. In thiscase, an operation according to the HT method took place between theareas having the normal threshold voltage and the areas having thethreshold voltage higher than the same.

When the height h2 was tapered in the direction away from theprotrusions 231A, the threshold voltage in the areas in a face-to-facerelationship with the protrusions 232 was slightly decreased.

While the above embodiment was described on an assumption that thealignment controlling structures were protrusions constituted bydielectric bodies on electrodes, it is possible to use electrode slits216 which are local blanks in electrodes in a display area as shown inFIG. 57A instead of the protrusions constituted by dielectric bodies.

FIG. 72 shows a modification of Embodiment 6-2. The present modificationis configured by replacing the protrusions 231A and 232 in theconfiguration of Embodiment 6-2 in FIG. 72 with an electrode slit 262which is provided on a pixel electrode 215 on a TFT substrate 205 andfine slits 263 having a pattern corresponding to the protrusions 232provided on both sides of the electrode slit 262 as illustrated.Protrusions 231 corresponding to the protrusions 231B are provided on aCF substrate 202. As a result, effects similar to those of Embodiment6-2 are achieved. However, the amounts of changes in the thresholdvoltage caused by the structures are smaller than those in a casewherein protrusions constituted by dielectric bodies are provided onelectrodes as in Embodiment 6-2.

As shown in FIG. 73, it is also possible to use recesses 252 that aredepressed parts of dielectric layers 251 and 252 provided on electrodes241 and 242 on substrates 202 and 205, the recesses being sunk indirections opposite to a liquid crystal layer 204. However, thearrangement is less effective compared to protrusions constituted bydielectric bodies provided on the electrodes.

The invention is advantageous when applied to vertical alignment (VA)type displays and, in particular, multi-domain vertical alignment (MVA)type displays, and embodiments described above are applications of theinvention to MVA type liquid crystal displays. However, the idea ofallowing flexible control of T-V characteristics (gradationcharacteristics) using an area ratio between areas having structurestherein can be applied to any type of liquid crystal display.

As described above, the present mode for carrying out the inventionmakes it possible to control T-V characteristics (gradationcharacteristics) freely by forming areas having different thresholdvoltages in one pixel. There is a little limitation on the ratio betweenthe areas, and an arbitrary ratio can therefore be set easily. Desiredcharacteristics can be achieved by making small changes in designvalues. Further, such a setting can be made with substantially noincrease in manufacturing steps.

In the present mode for carrying out the invention, the viewing anglecharacteristics of a liquid crystal display can be improved to make themclose to the characteristics of a CRT, and the range of application of aliquid crystal display is thus expanded.

1. A liquid crystal display comprising: a pair of substrates provided opposite to each other; a plurality of divisional areas which are a plurality of divisions of each pixel arranged on one of the pair of substrates, wherein a plurality of the pixels are aligned in a column between adjacent drain bus lines, and further wherein the liquid crystal display includes a plurality of said columns; a plurality of gate bus lines provided on said one of the substrates; a pixel electrode formed at each of the divisional areas; a first thin film transistor driving a first of the divisional areas and a second thin film transistor driving a second of the divisional areas, wherein said first and second thin film transistors are both electrically connected to the same gate bus line, and further wherein both said first divisional area and said second divisional area are located in the same one of said columns; liquid crystal molecules sealed between the pair of substrates; and a polymer, formed between said substrates, wherein said polymer determines directions in which the liquid crystal molecules tilt, wherein the pixel electrodes formed at each of the divisional areas are electrically insulated from each other or the pixel electrodes formed at each of the divisional areas are connected to each other through a high resistance, and wherein a first threshold voltage of liquid crystal molecules within said first divisional area is different from a second threshold voltage of liquid crystal molecules within said second divisional area.
 2. The liquid crystal display according to claim 1, wherein a first pre-tilt angle is the only pre-tilt angle defined within said first divisional area and a second pre-tilt angle is the only pre-tilt angle defined within said second divisional area.
 3. The liquid crystal display according to claim 1, wherein a first pre-tilt angle is obtained by radiating UV light while applying a first voltage to the liquid crystal molecules of the first divisional area and a second pre-tilt angle is obtained by radiating UV light while applying a second voltage to the liquid crystal molecules of the second divisional area, and further wherein the first voltage is different from the second voltage.
 4. The liquid crystal display according to claim 1, further comprising: a first storage capacitor bus line forming a first storage capacitor (Cs1) with the pixel electrode of said first divisional area; and a second storage capacitor bus line forming a second storage capacitor (Cs2) with the pixel electrode of said second divisional area, wherein the following is satisfied: Cs1/(Cs1+Clc1)≠Cs2/(Cs2+Clc2), wherein Clc1 is the liquid crystal capacitance of the first divisional area and Clc2 is the liquid crystal capacitance of the second divisional area.
 5. The liquid crystal display according to claim 1, wherein each pixel is defined by an area bordered by a pair of adjacent ones of said gate bus lines and a pair of adjacent ones of said drain bus lines.
 6. The liquid crystal display according to claim 1, wherein a threshold voltage difference between the first and the second divisional areas is 0.3 V or more.
 7. The liquid crystal display according to claim 1, wherein a threshold voltage difference between the first and the second divisional areas is 0.5 V or more.
 8. The liquid crystal display according to claim 1, wherein a threshold voltage difference between the first and the second divisional areas is 0.7 V or more. 